V. C. Andrews' series tend to have this. There are various reasons for this, but one main one is that VC Andrews had become ill and died before several of her series can be completed, and a ghostwriter completed the series. An example is in Flowers in the Attic, by Andrews, numerous things are referenced or mentioned by Corrine, only to be either retconned or changed in the prequel Garden of Shadows, which was written by a ghostwriter.
The ghostwriter has done this in his own series. For instance, in the Landry Series, Ruby's mother is named as Gabrielle in the first three books and Gabriel (a masculine name) in the last two. Her account of her own death also differs from the description that Grandmere Catherine gave.
Albert Campion In 'More Work for the Undertaker', Renée Roper greets Campion by name. However, when they met before (in 'Dancers in Mourning') he had avoided giving his name, allowing her to assume that he was a former lover of her late tenant Chloe Pye who didn't want his wife to find out about the affair.
Alice, Girl from the Future. As the series spanned several decades, it was clearly always adapted for modern audiences. But worse, the author claimed he never reread books after publication, and it shows. The action takes place in the 21st or maybe the 22nd century. Communism rules the world, and there's no money. Traveling to Sirius is a month long expedition, except a ship that travels through entire sectors in weeks is written off as obsolete and slow. The Tunguska Event was a failed Time Travel attempt, except two researchers later find it was a regular comet. The main villain is a shapeshifter, or a hypnotist, or disguises himself with masks and costumes. And these are only the major cases. Fans have concluded that the books describe several parallel worlds — hence all the contradictions.
In the first book, Visser Three snidely comments that it's an honor to meet Elfangor right before killing him. This directly contradicts the backstory concocted later on, wherein the two characters have extensive history. This can't even be attributed to the weird timeline/memory changes that happen near the end of that backstory, since it's alluded to in Visser.
Animorphs has quite a few of these in the first few books, with one of the more obvious being Jake using thought-speak on Tobias when Tobias is a cat and Jake is still unmorphed. Later books have them discuss the inability to use Thought-speak outside of morph. They're known among fans as Katherine Applegate Screw Ups or KASU's.
Book 34, The Prophecy, features Aldrea from The Hork-Bajir Chronicles returning due to her personality being recorded before her death. Trouble is, she's consistently referred to in the book as having voluntarily trapped herself in Hork-Bajir morph, when The Hork-Bajir Chronicles made clear that it was accidental as she was knocked out past the two hour time limit. Hell, the book can't even keep continuity within itself, as Aldrea announces right away that she doesn't know where the MacGuffin du jour is, but when she brings this up later, everyone acts like they're hearing it for the first time.
When Piers Anthony re-introduced several Adepts in the second Apprentice Adept series, their powers had changed from their original appearances, while ostensibly being the same characters:
Adept Green changed from using gestures and hand signs to work his magic to being a fire mage. This seems to be based solely on a scene in Juxtaposition, where a wall of flame warns Stile and Lady Blue away from Green's territory.
Adept Yellow changed from being the potions mistress of the Adepts to being a Beastmaster. Capturing animals and selling them off to others was a side practice of Yellow's in the original (Which she did with the use of a potion that lured them into her territory).
Adept Tan's Evil Eye was first shown as being as magically versatile as any other Adept's talent, limited only by line of sight. In the second, Tan and his twin children possessed the Evil Eye as a means of just mind control.
In Aunt Dimity's Death, Bill tells Lori that his mother was struck and killed by a bus when he was twelve, even giving this as the reason his father avoids public transport. In Aunt Dimity and the Village Witch, Jane Willis is said to have died after a long bout of cancer. Unlike the Backstory of Derek Harris and his fraught relationship with his father, there is no secret that Willis Sr. kept from his son; the author readily admits this was a mistake on her part.
In The Bartimaeus Trilogy, it was established that certain commoner children are whisked from their homes to be apprenticed to a magician, and forget their family and even their name. Yet Arthur Underwood has a desk that's "a family heirloom", and a photograph of his grandmother in his study. Also, in The Amulet of Samarkand, Arthur says Bartimaeus would have to be a djinni of "at least the thirteenth level", yet later he is described as fourth-level. And later as sixth level. On the other hand, Arthur's magical abilities are held in contempt by pretty much everyone (including his twelve-year-old apprentice), so that's not quite as bad (and depending on where the information on Bartimaeus' levels came from, spirits do enjoy inflating their own reputations and deflating their rivals').
The Book of the Dead can't seem to decide what colour Constance's eyes are; at the beginning of the book, they're violet, at the end of the book, they're blue, and in the preview for the next book, they're "dark".
Earlier Andrew VachssBurke books said that badass martial artist Max the Silent was a Mongolian, but the first mention of his nationality in Terminal has him as Tibetan. It's even more messed up when the next time says he's Mongolian again. Supposedly the Tibetan thing is established in the first book, but as later books never spell it out clearly in full, you can see how this confusion arises.
Children of the Red King: When Lysander's mother appears in book three, she's named Jessimine. In book five, she's named Hortense, which was the name of one of her daughters.
The Chronicles of Amber wobbles back and forth on a number of things over the course of its 10 books. Most notably, which of the royal family are full-blood siblings (Corwin initially says he and Random are; this is then changed to Corwin and Eric) and how time works around the Courts of Chaos. It's established at first that a short time anywhere else is a long time in the Courts, allowing for there to be nearly-adult children of couplings that happened mere days earlier. Later when Corwin actually goes there, a subjective hour or so in the Courts turns into several days back in Amber.
Word of God is that, like the landscape and the land itself, time is, well, Chaotic in the Courts, and changes how it flows in relation to Amber and Shadow frequently.
In The Chronicles of Narnia, Aslan tells people on various occasions that "no one is ever told what 'would have happened'". The wording is unequivocal. Then in The Magician's Nephew he tells someone "what would have happened". He even uses those very words. It may be writer error. On the other hand, he created Narnia, has used deception before (in The Horse and His Boy, he deliberately tricks Aravis), is "not a tame lion" (he doesn't usually follow any rules but his own), and the decision in question was one of the most important ones in Narnia's history. The situation is also unique in that "what would have happened" would all have been caused by a magical effect rather than For Want of a Nail, and Aslan doesn't reveal more than anyone else who was familiar enough with said magic could have predicted.
Book 1 has Boddy owning and skillfully playing a Stradivarius. However, two later books (#9, where he gets a solid gold trumpet, and #14, where he gets a Stradivarius) indicate that each instrument purchased is his first, and he's a Dreadful Musician.
Pizza is discussed in two books - book 10's chapter 2 ("Baby Booty"), and book 14's chapter 7 ("To Top It Off"). In the former, Mrs. Peacock expresses a distaste for pizza (since you eat it with your fingers), and Miss Scarlet wants hers with pepperoni. In the latter, Mrs. Peacock has no problem with pizza in general (though she shuns any topping other than cheese), and Miss Scarlet insists on only eating vegetarian toppings.
Stephen King made a minor error in Cujo. The father, Joe Cambers, is described as having blue eyes on one page, and brown eyes on the next. There's no supernatural explanation for this, it's just an error.
At one point in "The Body," Gordie says that Chris hasn't told Vern or Teddy anything about the pistol he has hidden in his bedroll. Apparently King forgot that earlier in the story, Chris tells Vern and Teddy about Gordie shooting the pistol that day behind the Blue Point Diner and they have a discussion about why they might need it.
The Dirk Pitt Adventures novels by Clive Cussler all take place in the same continuity, with past events often mentioned. At the end of Trojan Odyssey, Dirk marries congresswoman Loren Smith, his love interest for most of the series. In the preparations for the wedding, it states the Loren's parents flew out to attend. The plot of Vixen 03 revolves around the murder of Loren's father twenty years previously, and it was stated that he was already a widower when he died.
There's a few in the Discworld novels. A lot of the continuity errors are explained retroactively in Thief of Time — the History Monks have had to repatch history several times, and it tends to have some effect on the present as well. PTerry said in interviews, "There are no continuity errors, only alternate pasts."
Apart from the characterisation of Death and the Patrician, there's things like the gates of the Assassins' Guild which in Pyramids never close because Death is always open for business (and also because they rusted years ago) but are firmly closed at the end of Men at Arms.
The confusion in the early books about who trained the young Esme Weatherwax is eventually resolved when she explains she went round all the local witches and basically bullied them into teaching her.
It was also explained in a later book that Anthropomorphic Personifications take on human characteristics if they spend too much time around people; Death, what with keeping Ysabelle and Albert around so much, and studying humans actively, was certainly exposed to them and so changed and grew in personality.
It's been suggested that the fact Liessa Wyrmbidder suddenly becomes Lianna in her last mention during the Pern parody section of The Colour of Magic is an intentional nod to the below-mentioned Dragonriders of Pern naming errors. According to Sir Terry Pratchett it was a typo that crept in during the printing process.
The Divine Comedy: There's mention of Tiresias' daughter being seen in Limbo, even though she was earlier given a long time in the spotlight of the fourth ditch of Hell's eighth circle. No probable explanation has been offered for why she was bilocated in the First and Eighth Circle besides the former placement being one of Dante's only errors.
In the short story collection Short Trips: Time Signature, there's a bit of confusion about the Doctor's companion Isaac/William. He's first introduced in "An Overture Too Early" by Simon Gurrier (the book's editor) as Isaac, a defector from the USSR during the UNIT era, who claims to be a past companion of the Doctor although the Third Doctor realises that this is in his future. He later appears in "Fishing Trip" by Ben Aaronovitch as William, a young man from present-day Slough who the Sixth Doctor takes fishing. This gets tied together in "The Earwig Archipelago" by Matthew Sweet, in which William takes the name Isaac when he gets involved in local politics in a 1950s Ruritania, at which time the Doctor loses track of him. But between these stories, in "Walking City Blues" by Joff Brown, William refers to "the men who run the bureaux back home", suggesting that Brown missed that William didn't originally come from Eastern Europe.
It's understandable, since the books must have been mostly written simultaneously, but in the Eighth Doctor Adventures novel Dreamstone Moon, it's mentioned Sam spent some time teaching herself to use 23rd century computers including the "bowlboards" that have replaced keyboards, and in the next book, Seeing I, she panics when she realises a 23rd century keyboard isn't QWERTY.
And at the end of Seeing I, DOCTOR, the AI based on the Doctor's mind, is joined on its own adventures by FLORANCE, an AI from the Doctor Who New Adventures. Unfortunately, Seeing I is set in 2205, and the NA SLEEPY had established that FLORANCE had become the property of an evil Mega-Corp in 2180, and remained captive in their AI lab until 2227. Both books were by the same author.
Doctor Who Novelisations: The novelisations weren't really intended to be read end-to-end as a series, and attempting to do so will turn up some interesting continuity anomalies.
The earliest, and one of the most famous, is that Ian and Barbara meet the Doctor for the first time two novels in a row: Doctor Who and an Unearthly Child is the novelisation of the first TV story, and includes the scene of their first meeting; Doctor Who and the Daleks, the novelisation of the second TV story, was the first novelisation actually published, and was consequently rewritten to be Ian and Barbara's first adventure, with a new first-meeting scene at the beginning.
The second most famous example was that Doctor Who and the Doomsday Weapon, based on the TV story "Colony in Space", has the Doctor and Jo meeting each other for the first time at the beginning, reusing not their actual first meeting from "Terror of the Autons" but the scene later in that story in which the Master hypnotises her and sends her into UNIT HQ with a bomb.
The novelisation of "The Faceless Ones" has the Doctor use the sonic screwdriver in a scene where he didn't in the TV version. In the novelisation of the following story, "The Evil of the Daleks" which follows on immediately, without the Doctor having been back inside the TARDIS in the interim the Doctor notes that he hasn't got his sonic screwdriver because he left it in the TARDIS.
The novelisation of "The Dominators" faithfully retains the serial's cliffhanger ending, in which the TARDIS is threatened by an erupting volcano on the planet Dulkis. The novelisation of "The Mind Robber", which immediately follows, relocates the volcano to Earth. In turn, "The Mind Robber" novelisation ends with four people on board the TARDIS; by the start of "The Invasion" novelisation, which again should follow without a break, there are only three. (This also happens on TV.)
Doctor Who and the Space War, the novelisation of "Frontier in Space", removes the cliffhanger ending of the Doctor being shot... but he's still injured at the start of Doctor Who and the Planet of the Daleks.
The "Twice Upon a Time" novelisation uses the First Doctor's televised regeneration, as did the TV story, rather than the extended version used in the novelisation of "The Power of the Daleks", or the alternate one used in the novelisation of "The Tenth Planet", where Ben and Polly find the Second Doctor in the TARDIS's sleeping compressor.
Don Quixote: For a book that only has one continuation, there are various examples of those errors. Then again, Cervantes was mocking [those fans who put too much attention to continuity].. There are two types:
Sancho talks about using a sword at Part I Chapter XV and the Barber mentions Sancho has a sword in his hips at Part I Chapter XLVI, but at Part II Chapter XIV, Sancho denies ever having a sword.
The name of Sancho's wife changes at the same page in Part I Chapter 7 (Juana Gutiérrez and Mari Gutiérrez), and the same at Part II Chapter V (Teresa Panza and Teresa Cascajo) and in Part II Chapter L, Teresa Panza).
In Mercedes Lackey's Dragon Jousters cycle, the only one of Kiron's sisters whose name is given is the one who was so severely beaten by soldiers in the backstory as to cause permanent brain damage. However, at one point in the first book, Kiron remembers her name as Deshara; barely a page later, her name seems to be Dershela. And in the fourth book, when we finally meet Kiron's missing-presumed-dead mother and one of her daughters (and the apparent brain damage strongly implies that it's the same daughter), her name is Iris.
There are also a large number of dragon riders Kiron trains starting in the second book. Most aren't given much in the way of personality. In successive books those personalities are not kept straight, with Gan taking on Oset-re's traits and Oset-re not having any himself.
In the first book dragons are noted to eagerly devour any scorpions they find, seeing them as special treats. In the last book they are too small for dragons to notice, so a scene with a flood of scorpions has two dragons ignoring the creatures entirely instead of licking them all up.
The year number got muddled when The White Dragon was published (15PP when it should really have been 13PP), and subsequent prequel books made this problem impossible to fix without messing up the chronology of the stories. The two main side-effects of this are that it means F'lessan somehow became a Candidate while two years underage, and Mirrim's Path took four years instead of two to become fully mature.
Character names - both major and minor - frequently end up changing between books (and sometimes in the same book). The worst example of this happening is probably that Lord Larad's wife's name strangely changes from Dulsay to Janissary in All the Weyrs of Pern and back to Dulsay again in The Skies of Pern. Also, T'bor's dragon gets referred to as both Orth and Piyanth in Dragonflight.
In a few instances, a dead character has ended up appearing in a book that takes place after their death. Lord Oterel offers his support to young Readis in The Dolphins of Pern, despite a major part of the previous book dealing with people choosing his successor after his death.
In Dragonquest, Fandarel claims to have no sons. In Renegades of Pern, which takes place only a few years later, he apparently not only has four off-screen sons, but Piemur ends up in a relationship with his adult granddaughter.
Kim Delaney does get some mentions later on, particularly regarding the appearance of Harry's spirit-daughter in Skin Game.
Molly Carpenter is Dresden's first apprentice as sanctioned by the White Council. Kim Delaney was a minor practitioner he tutored, but she wasn't a member of the White Council and didn't have the magical talent to ever qualify, so they didn't consider his relationship with her relevant to his professional career. Dresden himself, however, did refer to Delaney as an apprentice nonetheless.
In Grave Peril, the name of the woman Bianca killed in Storm Front changes back and forth between Paula and Rachel, though this may be due to the fact that Paula was a pseudonym adopted due to her working in a brothel.
In Dead Beat Harry shoots one of the three main villains in the face, in the subsequent book it's always described as in the back of the head.
In Proven Guilty, the narration describes a family's minivan being crushed flat, with the next chapter mentioning the whole family piling into the same minivan.
In Ghost Story, a gunman's weapon changes from a snub-nosed revolver to a semiautomatic between chapters.
Michael at one point says he has no medical skills, and several books later says that he served as a medical corpsman.
In Skin Game, Anna Valmont says she was previously hired by Nicodemus to find the Shroud of Turin during the events of Death Masks. Actually, she was hired by Marcone. Nicodemus stole the Shroud as she attempted to make the sale, she was never in his employ.
At one point, Dresden considers talking to Butters about the Black Council, but decides to keep it to himself, forgetting that he already told Butters about them in Cold Days.
When Dresden visits the Brighter Future Society, he remarks that he's never been there in the flesh (his spirit visited during Ghost Story while his body was healing on Demonreach). However, he actually did go there in person at the end of Skin Game to speak with Mab and Marcone. He also can't seem to decide whether it's the Brighter Future Society or the Better Future Society, switching between the two throughout the book.
Ebenezar calls Dresden's new staff "rough work". Dresden defends himself by claiming he had to make it without sandpaper, directly contradicting a description in Skin Game of Dresden using leftover sandpaper from the dock he'd built on Demonreach. Possibly an in-universe lie, but Dresden's internal monologue doesn't indicate this.
From the comics, the Leanansidhe shows up in Wild Card, which takes place in between Small Favor and Turn Coat. This is a problem because up until Changes, Lea is imprisoned in the ice garden atop Mab's fortress of Arctis Tor in order to purge her of Nemesis.
In Unnatural Issue, Susanna makes a charm bundle and uses it to create a doppelgänger of herself so she can sneak off to practice magic. When she runs away from home she's specifically described as burning the bundle and scattering the ashes, as it could be used against her if it got into her evil father's hands. Yet towards the end of the novel it's said that the bundle could not be destroyed by mere burning as it was a magical object and Susanna still had it with her conveniently, as the good guys could then use it in their plan to draw out dear old dad.
The Elric Saga: Elric's mother died giving birth to him, according to Elric of Melniboné. However, in The Sailor on the Seas of Fate he reminisces about his parents in a way that suggests that his mother as well as his father was still alive at a time when he was old enough to remember her.
In the Flashman series, Flashman has an uncle Bindley who works at an office responsible for assigning military commissions, and at a couple of points, Flashman is forced to seek his help getting a commission. Consistent in the books is that Bindley dislikes Flashman, but the reason for this depends on the book. In the original novel, Bindley is from the aristocratic side of the family and doesn't like Flashman because he's from the commoner side. Later books reverse this by having Bindley as the commoner and resenting Flashman, who looks down on him. It's possible that this is a deliberate use of Unreliable Narrator, since the novels are supposedly extracts from memoirs Flashman wrote as a very old man.
In the Garrett, P.I. series, Glen Cook once had his sleuth refer to his stable-keeping friend Playmate as "Sweetheart". Cook later justified this, having Garrett mention how he'd once made it a practice to call Playmate by an alias, to divert the attention of some thugs who might make trouble for his friends.
In Gods, Nikita's mother is called Lilianna, while in The Girl, it's Irena. Admittedly, as an assassin, Irena likely has several names.
Ernest only obtained his middle "e" sometime between Gods and The Girl.
In Gods, Nikita and Kosma are described as twins, with Nikita being Kosma's Cool Big Sis and Irena/Lilianna taking both of them away when she ran from Ernest. In The Girl, they're half-siblings instead, with Kosma being older than Nikita (and Irena) by several hundred years. Their sibling dynamic is also reversed.
Also, Harry fails to notice the Thestrals pulling the carriages at the end of Goblet of Fire, immediately after he saw Cedric die, only to do so at the beginning of the next book. J.K. Rowling herself says that this is because she didn't want to add the Thestrals at the end of a book, stuffing it. Her in-universe explanation is that takes some time to "process" a death and come to terms with it; only after then can you see Thestrals.note This is not a continuity error from the start of the series because Harry didn't see his parents die at all, not even his mother. He was lying in the crib and only saw green light fill the room. Both J.K. Rowling herself and the seventh book confirm this. Link.
In the first book, Voldemort tells Harry that his father "put up a courageous fight" before he died, and had no reason to be lying to Harry at this point. Seven books on, we see this death in flashback: though James did try to hold Voldemort off, he was killed very quickly, having forgotten his wand. Perhaps, given that he was going against the Evil Overlord unarmed, instead of begging for mercy, Voldermort would have considered fighting him at all to be brave. He didn't say he was a tough fighter, just a brave one.
In Harry Potter and the Goblet of Fire, Harry and Voldemort duel, and because their wands are made from the same source (Fawkes the Phoenix), it creates a Phlebotinum effect that causes the spells Voldemort cast to pop back out of his wand in reverse order. An early edition of the book suggested that Harry's mother was killed before his father, which contradicted every description of their final moments. Rowling later admitted the mistake. Later versions of the book, and the movie, fix this.
The Death Eater called Rookwood has the first name Algernon in early editions of the book he's first referred to in, Goblet of Fire; it changes to Augustus in Order of the Phoenix. Later editions of Goblet have corrected his name to Augustus.
Sirius stated that Bellatrix Lestrange was a friend of Severus Snape's during their Hogwarts years, but according to the Black Family Tree Bellatrix is about 9 years older than both Sirius and Snape and would've graduated from Hogwarts before they even started. The Black Family Tree has many other errors such as both Bellatrix's father and grandfather having been only thirteen when they had their children,note Although if the Blacks are as messed-up a family, and as obsessed with breeding as they appear, this is actually not impossible, just oddly dark. Araminta Meliflua's exclusion (Sirius points to her name in the book), and Sirius's "aunt" Elladora being born many generations before with wizards' long lifespan he could still conceivably have known her, and colloquially called her his Aunt, but this is unlikely to have been Rowling's actual intention.
When visiting Hogwarts for the Triwizard Tournament in the fourth book, Molly Weasley mentions the previous gamekeeper before Hagrid, a character named Ogg, while reminiscing about her time at Hogwarts. This becomes a problem when we learn that Hagrid became the gamekeeper immediately after he was expelled in the early 1940s which was before Molly's time. It's possible however that Hagrid was not the only gamekeeper and became an assistant or apprentice gamekeeper under Ogg. He was only 14 when he was expelled, after all.
In Goblet of Fire, Harry gives the Marauder's Map to Mad-Eye Moody and is never mentioned as getting it back, but Harry suddenly has the map again in the next book. According to Rowling, Harry snuck into Moody's office to retrieve it, but she forgot to include this at the end of the fourth book.
In Chamber of Secrets, Percy says he'll have to take points from Gryffindor after catching Ron coming out of Moaning Myrtle's bathroom, but in Order of the Phoenix after Malfoy takes points away from Gryffindor for Hermione badmouthing Umbridge, Ernie Macmillan says prefects can't dock house points. Later editions changed this to say that prefects can't take points away from other prefects.
Rowling at one point said that Dumbledore was around 150 and McGonagall was roughly 70, however she's since said that Dumbledore was born in 1881 (making him 115-116 at death) and McGonagall was born in the 1930s.
The Pottermore website is supposed to give information that was All There in the Manual, but some of it is hard to reconcile with the books. For example, the site says that Voldemort possessed Quirrell as soon as they met...but Quirrell is able to shake hands with Harry in Diagon Alley (where he isn't wearing his turban), and his dialogue implies that Voldemort starting Sharing a Body with him after the failed Gringotts break-in (after which he is wearing the turban).
Similarly, in the Distant Epilogue (set in 2017), James Sirius sees his godbrother Teddy and cousin Victoire kissing and is completely shocked. Pottermore has Rita Skeeter articles set in 2014 that characterizes them as Make-Out Kids. So apparently the two were not only dating, but making headlines for three years before James had any idea that the two were an item? Possibly justified by Rita being a known liar, but even then her accuracy and James' obliviousness is a bit odd. One possible explanation is that James, who probably hadn't started into puberty yet, thought the act of kissing itself was shocking and noteworthy.
The first book strongly implies that Professor Quirrell has been the Defense Against the Dark Arts teacher for a while—Hagrid says he was fine when he was studying out of books, but then he "took a year off" to gain some practical experience and had some bad experiences, leaving him "afraid of his students" and "afraid of his subject". Book six specifies that ever since Voldemort was denied the DADA job many years before, Hogwarts has never been able to retain a DADA teacher for more than a year, because Voldemort put a curse on the job. This was later rationalized as Quirrell having been a teacher in a different position (namely, Muggle Studies) before he took a year off and returned to Hogwarts as the Defence Professor.
The chronology of the Tedrel Wars and Selenay's early reign is set in Exile's Honor and Exile's Valor. Skif's teacher in Take A Thief claims to have been crippled at the beginning of those wars, but according to him they started at least 15 years before the dates in the "Exile's" books.
The first two novels of the Mage Storms trilogy cover less than a year of time. Tremaine manages to age from around 30 years old at the beginning of "Storm Warning" to 45 years old in "Storm Rising". Another inconsistency in those novels is the official cult of the Eastern Empire, which goes from the "Forty Little Gods" to the "Hundred Little Gods".
The timeframe in which Selenay's first husband and father-in-law die changes continuously. When the series was first written, it was implied that the two died at roughly the same time with the notifications of their deaths crossing en route. In By The Sword, it was stated that learning about Thanel's attempted assassination of Selenay was a contributing factor to his father's decline and death. In Exile's Valor, Thanel's father dies about a year before Thanel himself does.
The Heroes of Olympus has a minor one. In The Lost Hero, Piper's dad has an assistant named Jane. In House of Hades, her name was Jessica instead. Rick Riordan joked on Twitter that "Her name is Jessica Jane. JJ to her friends." Then he admitted that he just plain forgot.
Horatio Hornblower has permanent powder burns on his hands from his old adventure in capturing the Castilla. The details of this seem to change every time the story is told. Even which hand is burned is inconsistent. In Beat to Quarters, he mentions his right hand was burned during the Castilla's capture while he was a lieutenant, yet in the short story "The Hand of Destiny", which details the capture while he's a lieutenant, it's his left hand that's burned, and Hornblower and the Atropos, in which he's a post captain in command of the 20 gun Atropos (a post ship, the smallest ship to warrant a post of full captain), he aids in the capture of the Castilla in a completely different action from what's described in "The Hand of Destiny", and doesn't receive a powder burn to his hand.
Christopher Paolini, of Inheritance Cycle fame, gave Murtagh dark brown hair in Eragon, but his Adaptation Dye-Job in the movie seems to have confused the author enough for Murtagh to have a different hair color by Brisingr.
In early novel Moonraker, Bond is eight years away from compulsory retirement from "00" Section at 45. Subsequent novels certainly take place over a period of more than eight years.
Additionally, in Casino Royale Bond recalls facing off against enemy agents over a gaming table before World War II. However, his obituary in You Only Live Twice indicates that he joined the secret service after leaving the Navy in World War II, and that he enlisted at the age of 17.
The story "Bertie Changes His Mind" (reprinted in Carry On, Jeeves) revolved around the fact that Bertie was considering moving in with his sister and her family, although they never actually appeared. Later, in Thank You, Jeeves, Bertie is asked whether he has any sisters and replies in the negative.
Another example again involves Thank You, Jeeves, which features Mr. Stoker and his daughter Pauline. When Bertie asks Pop Stoker which daughter he's referring to in the course of conversation, Stoker replies, "I have only one daughter." A few books later we're introduced to a second daughter, Emerald Stoker. But then, one must not overthink these books.
The 2004 Justice League of America novel The Flash: Stop Motion by Mark Shultz seems to be set in then-current comicbook continuity. A significant plot point in the novel is Wally's "blood bond" to his Aunt Iris. The problem? In that continuity, Iris is adopted.
The first book, The Portable Door, stated that using the Door for a journey of more than an hour was almost impossible, and using it for any real length of time was exhausting. By The Better Mousetrap, Frank Carpenter is living his entire life about two decades in his past thanks to the Door, without really experiencing any negative effects whatsoever.
Earth, Air, Fire and Custard says that whenever bauxite was mentioned in the previous books, it actually meant custard, then ignores this and continues to refer to bauxite.
In the first book of The Land of Stories, the character Froggy claims he was cursed into a frog for being vain. In the fourth book, the story changes into him being cursed because his girlfriend thought he was breaking up with her for being ugly, when in reality it was because she was a witch.
In the seventh book of the Maximum Ride series - Angel, Maya says to Max, "Gee, I haven't seen you since you tried to kill me." The most recent time they met, in the third book - Saving The World and Other Extreme Sports, they were having a civilized conversation.
In The Angel Experiment, we discover that the Flock had parents, and Iggy's mom died, but his dad is alive. Fast-forward to School's Out — Forever, when who should show up but both his parents, alive and well and ready to make money off of him.
Unsurprisingly, considering the Loads and Loads of Characters and the insanely long hiatuses between books, The Obernewtyn Chronicles has a fair few. The most serious one occurs in The Keeping Place, where Elspeth and Kella talk about their previous experience of escaping the cloister in Sutrium, and Elspeth gives detailed information about its layout to Brydda. Only problem: none of them have been to the Sutrium cloister before. The cloister they escaped was in Aborium, on the other side of the country. Another error occurs in The Sending, where Elspeth spends the first third of the book resentful and bitter towards Kella because she didn't come to see Domick before his death, leading to an rift between the pair until Kella finally works it out and exclaims that she could not have come because she was never even told about what happened to Domick. Elspeth had actually already worked out the reason for Kella's absence in the previous book and bore no hard feelings over it, but it seems the author forgot this.
For example, in the first book, Percy dreams with a girl he has never seen before, but somehow already knows who she is. In the second book, he has a dream with the same girl, but is neither able to identify her, nor notice that he already dreamed about her before. And since the entire series is narrated through his point of view, it would be impossible for him to forget that first dream.
The third and fourth books of the Pit Dragon Chronicles were written 22 years apart. Many things that were important in the first three books are randomly changed in the fourth - such as a psychic connection between dragon and handler being taken for granted suddenly being a horrifying new idea, or dragons being Starfish Aliens mentally with mysterious degrees of intelligence suddenly just being animals.
In-universe in The Quorum, when a novelist character's mental breakdown is partly triggered by a critic pointing out that a major character in his novel series is described as having two different eye colours in different places.
In Taggerung, Sawney Rath has a nicer moment of genre savviness when he swears he won't be one of the many dead vermin lords who've attacked Redwall ...except that one of the names he drops is Ferahgo, who never went near Redwall. Then again, that took place the equivalent of several centuries earlier, and Sawney, being a vermin chieftain, would have been going off of oral legends, not the official chronicles of the Redwall recorders.
However, there is another one that's not so easily explained. In Mossflower, Bella the badger says that only male badgers make the journey to Salamandastron, but in Lord Brocktree, which chronologically took place before Mossflower, when Lord Brocktree is looking at some carvings of the previous badgers who ruled Salamandastron, one of the names mentioned is Spearlady Gorse. On the other hand, Gorse may have come long enough ago that she simply wasn't recorded in Bella's books.
Barlom from Outcast of Redwall states that he is the grandson of Timballisto and wishes Martin had lived long enough to have met him. The Legend of Luke states that Timballisto died shortly after the events shown in Mossflower, where Timballisto and Martin interacted on more than one occasion. Barlom says that he recalled sitting on his grandfather's knee though, making this impossible.
Dandin and later Bryony are both described as great-grandchildren of Gonff. This would make them either siblings or first cousins. Jacques later said that they were only "distantly" related though, as Bryony's story occurred earlier than Dandin's by chronology. Realistically, in either case this is hardly "distant". Bryony being an older first cousin of Dandin is probably the best bet for fans who want to ignore what Jacques said and go by the text (it's never said just how much earlier her story takes place after all, and this gives the timeline some greater leeway).
The Riftwar Cycle: The later novels have quite a few continuity errors. For instance:
Eric von Darkmoor mentioning that he had never married when he got married in Wrath of a Demon King.
The Tsurani Emperor appointing a Warlord in Wrath of a Mad God, generations after the title was abolished and replaced with a similar position with no attached political authority in Servant of the Empire.
In the same book, mention of House Minwanabi, every member of which had committed ritual suicide at about the same time as the position of Warlord was abolished.
The story Jimmy the Hand taking place in Land's End, resulting in virtually all of the nobility of that small region dying, which makes the long-established recurring minor character Squire Locklear of Land's End's backstory nonsensical, especially since his first appearance in the timeline is only about a year later, nowhere near enough time for the new Baron, who had no siblings, to marry, produce an heir, and have that heir grow old enough to be sent as a squire to the Prince's court.
When Abigail Kamara's father is first mentioned in Moon Over Soho, his first name is Adam. In the next book, Whispers Under Ground, he's Alfred.
Short story "The Home Crowd Advantage" is placed by the official chronology between the first two books, Rivers of London and Moon Over Soho. However, when Peter talks about why he's not part of the Olympics security at the beginning, he references an ambulance hijacking that takes place in Moon Over Soho, which isn't supposed to have happened yet.
Dr. John Watson of Sherlock Holmes seems to get caught in these rather often.
Watson served as an Assistant Surgeon of the Army Medical Department (attached to the 66th Foot) in Afghanistan, but was discharged following an injury received in the line of duty during the Battle of Maiwand. In a Series Continuity Error, his wound shifted from shoulder to leg. This is referenced in the Guy Ritchie film, where Watson limps throughout the film but is also wounded in his shoulder by shrapnel near the end, and in Sherlock, where he was shot in the shoulder, but has psychosomatic pain in his leg. Carole Nelson Douglas used this error to underpin the plot of her Irene Adler novel A Soul of Steel, in which Watson had to be saved from an assassin without informing him; according to her book, Watson received both injuries, getting the second wound in hospital while delirious from a fever, so he did not recall getting it.
Doyle's stories which sometimes assigned Watson a wife, sometimes didn't, and sometimes referred to Watson as a widower, never in chronology hopelessly confused the issue of just how many wives Watson had. W.S. Baring-Gould, author of a well-researched "biography" of Holmes, decided Watson had three wives. Others have suggested numbers up to six.
Both "The Final Problem" and its prequel, The Valley of Fear, involve Watson hearing about Moriarty for the first time. The latter apparently makes Moriarty aware of Holmes' activities against him two years earlier than the former does.
To add insult to floating injury, Watson's first name is in question. It's stated as John H. Watson at least once, but in "The Man With the Twisted Lip" his wife calls him James. Scholars (and the BBC series) have tried to get around this by expanding Watson's middle initial H to 'Hamish', the Scottish equivalent.
Professor James Moriarty seems to have a brother, Colonel James Moriarty. Doyle has a James problem.
In "The Adventure of the Blanched Soldier", Holmes refers to "the case which my friend Watson has described as that of the Abbey School, in which the Duke of Greyminster was so deeply involved". This seems to be intended as a reference to "The Adventure of the Priory School", but misremembering both what religious building the school was named after, and the title of the Duke of Holdernesse. (The Watsonian explanation for this is that Watson was using pseudonyms to avoid embarrassing a member of the nobility.)
In a clear case of the writer and editor falling asleep, in at least the original hardcover of A Song of Ice and Fire's A Feast for Crows, Princess Arianne discusses the implications of Lord Tywin's death and Cersei coming to rule. A scant three pages later, she is first informed about it happening.
Renly is first described as having green eyes, despite the fact that all Baratheons having blue eyes is a plot point (and his eyes are described as blue for the rest of the series).
In the Spellsinger series, Mudge the otter has kids as of the sixth book. How many, and what their names and genders are, changes from #6 (daughter Prickett and two sons) to #7 (son Squill, daughter Neena), and again to #8 (Squill and Nocter, genders not stated). Granted, Mudge isn't the most organized of fellows, but you'd think he'd keep track of who his kids are.
Star Trek: The Next Generation: Starfleet Academy contradicts Troi's early life depicted in Imzadi and the episode "Second Chances".
Star Trek: Voyager: Starfleet Academy contradicts Janeway's early life depicted in Mosaic.
Early in The Tamuli Emperor Sarabian considers beheading his Prime Minister - and when Queen Ehlana of Elenia asks under what charge, replies "This is Tamuli. I dont need charges. I can have his head chopped off if I decide that I dont like his haircut." The rest of the series makes much of the fact Sarabian is a powerless figurehead who has no say in the government, and needs Ehlana to teach him how to be a "proper" absolute ruler.
Happened towards the end of the Teenage Worrier books. Among other things, Hazel's name in the first book is Hazel Williams and she attends an exclusive school called St Mary's Academy; in the last, her name is Hazel Appleby and her school is St Cheyngangg's (with no mention of her changing schools).
In Protector of the Small's third book, Squire, Kel seems to jump from age fourteen to sixteen. It's also stated that her first tilt against Raoul was her first tilt against a live person when she'd already done that in Page (Pierce said she simply forgot). In Lady Knight, Raoul says that nobody has ever been allowed in the Chamber of the Ordeal twice except that it's a part of the coronation so Jon the knight king did in the first quartet, and Raoul is close enough to Jon to know that.
Early in the series it is established that Moroi monarchs have the right to choose their own successor. The only acknowledged limitation to this right is that they can not choose a heir from their own royal clan. That is why Evil Prince Victor Dashkov considered himself the most likely heir to Queen Tatiana Ivashkov. Because she was likely to choose him, at least until his fatal disease discounted him as a choice. In the Succession Crisis of Last Sacrifice it is instead established that the Moroi political system is an Elective Monarchy. So monarchs have no right to choose their successors after all.
Tatiana was murdered before she had a chance to name her successor, which meant that they had to go with the back-up option of the election.
There is a minor one, involving the powers of Jill. When introduced in Shadow Kiss, Jill tells Rose that she is an air user. She is later established as a water user instead, even given some training by older water user Mia Rinaldi. According to Word of God the first instance was a typo, and Jill's element is water.
The Vampire Chronicles is riddled with continuity errors, some of which can be written off due to the fact that different books have different narrators. However, it's hard to understand how Lestat's eye-colour, even self-described, keeps shifting.
In Queen of the Damned, Jesse Reeves sees spirits as a human but completely loses this ability when she becomes a vampire. It's made quite clear that vampires do not possess this ability. In the next book, Claudia's ghost appears to Lestat... well, it's a ghost of a vampire so maybe the rules are different. However, Merrick becomes a vampire and retains her ghost-seeing abilities, which nobody seems to think is that unusual.
In Interview, Louis mentions that Lestat received help from another vampire by the same maker. Future novels show that he was the only one turned by Magnus. He also receives help from another vampire in New Orleans, though he makes no mention of him in his own novel. These may be explainable by the changing narrators.
In World Engine, the Necrons crumble to the ground when killed. This contradicts every single other piece of Warhammer 40K's expanded universe, where the Necrons either self-destruct or are teleported out.
Word Bearers has the Necrons cut off the Warp in a system. This includes Possessed characters losing their daemons, and gives the psykers an extremely bad time. Somehow, the Word Bearers are still able to use teleporters, which go through the Warp.
The Outcast Dead states that Magnus the Red warned the Emperor about Horus's treachery after the massacre at Isstvan V, contradicting every other book that put Magnus's warning coming before Horus's opening move at Isstvan III, including more than one written by the same author.
In A Thousand Sons, Ahriman and Magnus tell Lemuel Gaumon about the history of the Thousand Sons, including how other primarchs like Mortarion and Corax looked down on their psychic abilities before Magnus was discovered. Deliverance Lost shows that Corax was the second-last primarch discovered (Alpharius has always been the last one), so he couldn't have been around to voice his dislike of psychics.
Happens many, many times with the Warrior Cats seriesnote A full list of inconsistencies and typos can be seen here. Characters often change pelt colors and occasionally flip genders, sometimes they'll forget what certain characters know and don't know, time passage will be inaccurate, and some details about Clan life and the history of the Clans have gotten changed around. Seeing as there's dozens of books and side book, over a thousand characters, and multiple people writing the series, it's only natural that things get mixed up once in a while. Of note:
In Spottedleaf's Heart, Spottedkif wanted to be a warrior. According to Bluestar's Prophecy, she had wanted to be a medicinecat and begged Featherwhisker to make her an apprentice.
Speckletail is convinced to retire and become an elder after her son Snowkit is killed. However, Snowkit has a sister named Mistlekit who disappeared randomly. She's never been described as dead or seen as a warrior.
In Crookedstar's Promise, a gathering is disturbed because RiverClan brings up stolen kits. In Bluestar's Prophecy, WindClan brings up a fight with ThunderClan.
Mistystar's Omen says that Mudfur stayed in the old forest because he was too old to move. He had died before the journey began.
Graystripe calls Mistystar and Stonefur his kits once.
In Redtail's Debt, Redtail kills Oakheart. In the first arc, there was a big deal about how he hadn't killed him. Oakheart died in a rockfall.
The Well World series by Jack Chalker had a fair number. Some of these are explained by there being a very long time-gap between the early books and the later ones, so the author merely forgot the prior details.
Several of the books contain maps of sections of the Well World, and a careful look at them reveals that some hexes are named differently or in different places in different books.
And then there is the case of the hex that seems to contain 3 completely different main species. In one book, they are quadripedal lizards with excellent natural camouflage abilities. In another, they are bipedal magic-using. And in a third they are snake-like men with semi-invisibility.
And also a race that, despite having a major character being a member of the species, and their warlike battle lizard traits being a fairly large background plot point, by a later book, they are man-sized mosquito-like things.
Piers Anthony wrote Geis of the Gargoyle partially to explain and straighten out continuity errors that had crept into the chronology of Xanth.