The first two Discworld books are parodies of Sword and Sorcery fantasy. They featured a lot of elements that were quietly dropped in the later books, which are parodies of just about everything.
The shift in human naming conventions is particularly marked, with fantasy-parodic names like Zlorf and Gorphal giving way to conventional names like Fred or Sybil. Equal Rites saw the first ordinary surnames (the Smiths), and Mort (for Mortimer) was the series' first protagonist with a real-world given name.
Pterry is also more likely to Call a Rabbit a "Smeerp" in the early novels; Mort's father apparently farms "tharga beasts", and since (unlike vermine or republican bees in later books) nothing amusing is said about them to differ them from Roundworld animals, they might as well be oxen.
Much is made of Nobby Nobbs being a clothes horse in Guards! Guards! and having a wardrobe of the latest fashions that he wears off duty. By Feet of Clay, he has no idea what to wear to a posh party until Fred Colon tells him he can just wear his uniform.
Death actively, and with little reason, kills a man in the first book by stopping his heart. This goes directly against his personality in later books, as he knows fully well that people are supposed to die on their own time. Also, he rather likes people.
In very similar fashion the city of Quirm was originally generically 'foreign' in contrast to the British Ankh-Morpork; in fact before Genua became established as the Disc version of Italy Quirm itself was sometimes a stand in for things Italian (mention is made of a Pisan-style 'Collapsed Tower' and the Leonardo da Vinci analog is Leonard da Quirm). In later books it is very firmly fantasy counterpart France.
On Basilisk Station, the first Honor Harrington novel, has a bit of this. The extremely short-ranged Grav Lance that is one of the central plot elements of the book is gone from later installments, as weapon ranges extend from tens to hundreds of thousands to hundreds of millions of kilometers, and while Admiral Dame Sonja Hemphill remains quite enamored of her own genius in her later appearancesnote and not undeservedly, given that her technological breakthroughs include faster-than-light communication, multi-drive missiles, and FTL missile control, plus a host of others, she is not (unlike in the first book) inclined to take out her frustrations over the failures of systems she developed on the officers trying to employ them in the field.
The first Redwall novel, Redwall, features a number of references indicating that the animals live in a world where humans also exist, such as a horse cart, a church, taverns, ports, and a direct mention of Portugal. Also, one of the characters was a beaver. In later books, author Brian Jacques made it clear that only animals existed in the Redwall universe, and only animals native to the British Isles, so there were no future appearances of any more beavers (though beavers WERE native to Britain at one time, but they were killed off due to overhunting). And when animals that aren't native to Britain do appear, like the golden hamster in one book, they speak with foreign accents to indicate that they aren't from Mossflower.
The animal characters also gradually became more human-like, especially badger characters. In the first book, specific note is always made when Constance rears up on her back feet; in later books, even badgers are assumed to be bipedal.
The order of Redwall itself started out as reminiscent of a Catholic monastic order: the members wore habits, they lived somewhat sequestered inside their Abbey, and remained celibate for the entirety of their lives. Cornflower got yelled at for flirting with Matthias, who was a postulant of the order and therefore off-limits; when they got married, Matthias was mentioned to have left the order and lived apart from the monks. In later books, all that's left of this rule is that there is an Abbey. Even Abbesses and Abbots can be married, and not even the habit is required anymore, morphing it into some sort of peaceful commune that's little different from other communities in the forest.
The first book Redwall had more religious/mystical references, including mentions of heaven and hell and a snake named Asmodeus, after a demon in the Catholic/Orthodox bible. Again, these are toned down in establishing Redwall as its own universe. In the first book, it is also ambiguous whether Sela the fox actually had unique powers. Later in the series, any claims of supernatural powers are explicitly presented as a Scooby-Doo Hoax.
In the first book of Piers Anthony's Xanth series, there are mundane animals like chipmunks and hawks in Xanth, and the animals have a Magic Talent just like most people do. The infamous puns are almost completely absent. Later on, Anthony decided that everything in Xanth either "had magic" or "was magic", and all animals and plants became of the "was magic" type.
Also, the first few books were dark in tone, and a genuine fantasy trilogy. Xanth started an exploration of a fantasy world where everyone has one specific talent. Then it got more parodic, more comedic, even cartoonish, and is now a full-blown Running the Asylum cash cow.
Sherlock Holmes displayed some mannerisms in the first story that were then dropped — most infamously, his claim that he deliberately forgot all facts that were irrelevant to his work, such as that the Earth goes round the Sun! (That particular fact doesn't turn up again, but he displays much more well-rounded knowledge in the rest of the series. At the very least, Watson's claim that Holmes knows nothing of politics is disproven by "A Scandal in Bohemia".)
A Study In Scarlet is also the only Holmes story to cut away to an omniscient narrator, rather than staying within the confines of Watson's knowledge. Players of the Great Game do a good job ignoring this.
Holmes’s cocaine habit is directly observed (canonically) only in The Sign of Four (1890) and "A Scandal in Bohemia" (1891), two of the very earliest works in the series. Watson states he made him quit much later in "The Adventure of the Missing Three Quarter".
Bill Bryson's The Lost Continent was written by an angrier, less mature Bryson and it shows. Readers who begin with later works might be surprised at how acidic, anti-American (and arguably elitist) Bryson was before he mellowed. Certainly he seems much less fond of his home town, Des Moines, and his father, and much more of a wannabe Brit.
The same could be said for Neither Here Nor There, published two years after The Lost Continent. It's certainly rougher and more acidic in tone than his later books.
To avoid these sorts of situations, LucasFilm had forbidden any EU works dealing with the pre-movie lives of Anakin Skywalker/Darth Vader, Obi-wan Kenobi or Yoda, even unto not allowing writers to identify the race or home planet of Yoda. Lucasfilm didn't say anything about Boba Fett, so some novelists decided to tackle him, only to need some industrial-strength retcon when the prequels came around.
The novelization of A New Hope has the same Early Installment Weirdness problems. The story is told from the point of view of a old chronicle, numerous scenes are added that were cut from the movie ultimately (including the Jabba meets Han scene added in special editions), Earth animals are commonly mentioned, Luke's squadron is identified as Blue Squadron (which was originally intended in the film, but due to SFX limitations was changed to Red), It also portrays the Emperor as a puppet of the bureaucrats, contradicting his usual characterization. Fittingly enough, both books were written by Alan Dean Foster.
Marvel Star Wars started coming out around the time of ANH, and its early issues show this trope. Not only did Vader and Chewie look weird, but Obi-Wan once advises Luke to use all of his anger in a Force attack on Vader, there was a world where Obi-Wan and his two apprentices, Anakin Skywalker and Darth Vader had visited, and a story about a Jedi, set in the past, had the Jedi wearing a space-fashion outfit.
Both David Eddings's Belgariad and Elenium series start off this way; eg. Belgarath's comment about "well then we'd have to wait another century for the circumstances to be right again" which is totally at odds with all the prophecy stuff from later books. Elenium begins with Sparhawk planning to quietly garrotte someone, which seems quite out-of-character later on; in general the first few chapters seem a lot darker than the rest of it.
The first Animorphs book contains several elements that are never mentioned again, such as the ability to broadcast your thoughts to a person in morph when you weren't in morph yourself, or the psychic Info Dump laid on Tobias by Elfangor.
The first one of those was addressed by the author as a mistake. She was unsure of how thought speech should work, and by the time she decided it was too late to change the first book.
And apparently she went too far the other direction when she had Ax declare, in an early book, that humans couldn't use thought speech at all (even if said human was actually an Andalite in morph), which admittedly doesn't make much sense. That, too, gets retconned away when Ax uses thought speech in human form in a later book.
In the first book, Elfangor seems like a psychic. He appears to be able to feel the kids' fear as they hide, and let them borrow some of his courage. Andalites are never portrayed with such abilities again, with their telepathy limited to communication.
Interestingly, this ability reappears much later in The Ellimist Chronicles. Apparently Andalites have always had this ability, but Elfangor is the only modern-day one to use it on-camera.
Also, Visser Three acts as if he's meeting Elfangor for the first time. ("Prince Elfangor-Sirinial-Shamtul if I am not mistaken. An honor to meet you..."). Now that we know better, from The Andalite Chronicles, we'll just have to assume he was being sarcastic.
A big part of the first book involves the heroes finding out who is a Controller because said person suddenly acted out-of-character. In later parts of the series, Yeerks make a point of acting very in-character, and it's even shown that, by accessing a person's memory, they are brilliant at acting the part.
This actually became an important plot point in the pilot episode of the show, as the Animorphs identify Chapman as a Controller because he maintains his habits even when no one is around, in this case, scratching his leg with his foot.
Hork-Bajir having a biological imperative to make war with each other every sixty or so years (later books indicate Hork-Bajir don't even live that long) and the warning that Yeerks have infiltrated the Andalite home world, which never goes anywhere.
In addition the early books mention several races said to be enslaved by the yeerks (i.e the ssstram, mak, and nahara) which are never encountered or even mentioned again.
The rules of magic seem to have not been quite worked out in the first book. Several spells are performed nonverbally and without wands, both of which are established to be extremely difficult in later books. Hagrid, despite having been expelled in his third year, is able to perform nonverbal spells, something which the main characters don't learn until their sixth year. He also successfully performs magic with a broken wand, something that the second book establishes is nearly impossible. Apart from the levitation spell, specific spells, their incantations, and their specific effects are not really brought up in the first book.
Regarding Hagrid's wand, it's implied that Dumbledore secretly used the Elder Wand to fix and transfigure it into the umbrella.
Hagrid being able to perform certain magic non-verbally is justified indirectly by Harry's actions in the third book. Whether the witch/wizard is of legal age or isn't, they sometimes can't control their emotions and intense emotions could result in unwanted performance of magic. Hagrid himself says in the first book that he shouldn't have done it, but he got so mad at Dursley...
None of the characters, not even those who were raised wizards, seem to know how Sorting works in the first book. In addition, Ron is fooled by his brother George into thinking a doggerel couplet is a spell which he could use to alter the pigmentation of Scabbers the rat, while all real spells seen in the books (after this example) are Dog Latin.
The school song, performed at the beginning of the main characters' first year, never appears in any other books. J.K. Rowling said that the school song is only performed whenever Dumbledore is in a good mood and feels like it. It's likely that with all the dark things that go on in the ensuing years, he just never feels up to it. A deleted scene in the Goblet of Fire film shows the Hogwarts student body singing it to the students from Beauxbatons and Durmstrang.
Other early books show a bit of this too, especially in terminology; Prisoner of Azkaban refers to "Hit Wizards", whose role is replaced by Aurors. At one point in the first book, Harry refers to "going over to the Dark Side" (obviously in the context of refusing ever to do such a thing). It's not until the fourth book that we learn that Voldemort's supporters are called Death Eaters and Ministry of Magic employees who hunt dangerous wizards are called Aurors.
Terminology is confused several times in early books. In the first book, Neville mentions that his family was worried he'd turn out to be a "Muggle", i.e. not have any magic, but from the second book on non-magical individuals born to magic parents are called "Squibs".
A minor example: Harry is dismayed to have lost "two points for Gryffindor in his very first week," both of which Professor Snape deducts in Harry's first Potions class. He will lose many, many more during his years at Hogwarts. Points in general seem to undergo inflation as the series goes on; where teachers took one or two points away for infractions in the first book, they commonly take five or ten for similar offenses in later books. Some deleted footage from The Film of the Book reflects this: Snape deducts Gryffindor five points when Harry can't answer his questions and refers him to the obviously much more eager Hermione.
There's also the Deluminator, which is only called such in the last book. When it appeared in the first and fifth, the narration referred to it as Dumbledore's "Put-Outer".
Early in the first book, Petunia claims Lily turned teacups into rats while she was home from school. Later in the same book, we find out Hogwarts students aren't allowed to use magic outside of school; Deathly Hallows confirms the rules haven't changed since Lily went to school. Rowling's answer has been that Petunia was exaggerating but Lily occasionally got warnings for out-of-school magic.
A certain character in Chamber of Secrets mentions Hagrid was raising werewolf cubs under his bed. In the very next book, it becomes clear that werewolves are humans afflicted with a disease that makes them become wolves during a full moon. JKR later said that the character in question was lying, which would be in-character, but is not made clear at the time. Perhaps as a callback to this, in the seventh book the same character refers to the hypothetical offspring of an heroic werewolf as "cubs", in a context that makes it clear that he's making a rather offensive joke.
In The Philosopher's Stone, the famous Quidditch scene is written partly from Ron and Hermione's perspective, and a short part of the giant chess scene is from Ron's point of view. Later books are completely written from Harry's point of view, except sometimes the first chapter or two of each book and the moments Harry sees in Voldemort's mind.
The "closeness" of the Muggle and wizarding worlds, in terms of how much the wizards knew about Muggles, seemed to be more fluid in the first book. In The Sorcerer's Stone, Malfoy is overheard telling stories about flying that always seemed to end with him narrowly dodging Muggles in helicopters. Even in the second book, it would have been a point of pride for Malfoy that he would have no idea what a helicopter was (although it's possible he might have been lying in order to make himself look good in the first book).
Ron is said in the first book to have a collection of comic books about a "mad Muggle," which would seem to indicate a level of fascination about Muggles that's notably lacking in the Wizarding World in the later books. Even the "Muggle Studies" course Hogwarts offers is implied to be unpopular.
Reading the first edition of the Brothers Grimm's Fairy Tale collection can be quite shocking for many people who are used to later editions. The stepmothers of Snow White and Hansel and Gretel are instead their biological mothers, Cinderella does not go to the first ball (instead watching it from the pigeon roost) and only goes to the second and third, and many tales of French origin appear that don't appear in later editions.
Steven Erikson's Malazan Book of the Fallen series shows marked differences between the first book, Gardens of the Moon, and the later books. (Examples include Tool's hundred-mile-diameter magic-deadening Tellann aura and the interaction of munitions with magic use, among many others.) To Malazan fans, this is known as a GotMism. The first book was written around a decade before any of the other ones.
Most people who've read The Wonderful Wizard of Oz these days know little of the numerous sequels that followed. They'd be shocked at how many of the rules were rewritten even between the first and second books. Issues such as the existence of money, the actual number of witches (and related magic users) in the land, whether or not the Emerald City is actually green, and if people can actually die were altered drastically over the first few sequels. No doubt this is because while the rules found in The Wonderful Wizard of Oz can work within the plot of that particular story, they proved too confining when others had to be written.
J. R. R. Tolkien's Middle-Earth shows this in two ways. Firstly, The Hobbit seems like a somewhat fanciful children's tale compared to The Lord of the Rings; Tolkien hadn't even decided it was going to take place in the context of his wider mythology when he originally wrote it. Though modern editions have removed some of the weirdness, earlier versions had oddities like a railroad in the Shire, and Bilbo musing about taking a trip to China. Secondly, many of his earlier drafts for said mythology have been published, and if anything they seem more fanciful still. By the way of an example, in one version Sauron's role in the story of Beren and Lúthien is played by an evil cat. Aragorn was originally a hobbit named "Trotter," so-called because he wore wooden shoes, and Treebeard was a villainous giant rather than a friendly ent. Balrogs were much more numerous and less powerful than they later became. Whereas in the final versions killing a Balrog has only been accomplished thrice, early drafts had the heroes killing them by the hundreds.
The Hobbit and the early portions of The Fellowship of the Ring are narrated in a chatty and snarky tone that sounds like the narrator from obvious children novels like Narnia or Mary Poppins; especially when compared to the "ye epic of olde" cadence of The Return of the King. This is because Tolkien originally wrote the Hobbit as a simple children's book, and The Lord of the Rings was (ironically, considering its current length) going to be a short sequel to that story. But the story "grew in the telling" as Tolkien said, and so the early parts of The Fellowship of the Ring, written while Tolkien still thought he was writing another children's book, seem far less solemn than what comes later. From a literary perspective this has the writing becoming more serious as the story becomes more serious - an interesting effect.
The Last Battle states that there are only two god-like beings in Narnia: Aslan and Tash. LWW, however, shows that Bacchus and Silenus occasionally dropped into Narnia to party with the fauns. Prince Caspian even mentions Pomona, the Maenads and a River God serving Aslan. These are later dropped as the series progresses.
The first book also had a more whimsical feel to it in regards to the Fantasy Kitchen Sink meets Anachronism Stew tone, what with Mr Tumnus's umbrella, Mrs Beaver's sewing machine and the infamous appearance of Father Christmas. Modern appliances weren't around in the later books.
In the first Star Trek: New Frontier book, written in 1997, prior to the trend towards consistency in the Trek novels (which started around 2001)), Danter is said to be a member of the United Federation of Planets. This seems rather odd, seeing as they're most definitely not what we'd expect from the Federation. Indeed, they're openly imperialistic. Later books seem to have retconned this, making Danter definitely an independent nation.
Over Sea, Under Stone, the first book of The Dark Is Rising, is a rather standard, almost Enid Blyton-esque children's adventure story, with less of the fantasy elements and references to Celtic mythology that defined the later books (they only show up in the second half of the book, and even then they're relatively subtle).
The first Fablehaven book is a mostly cheerful, good-natured, and lighthearted fantasy story about a pair of bickering siblings who discover that their grandparents run a nature preserve for magical creatures. The entire concept is treated with wonder. The later books in the series, however, are extremely dark, changing their tone entirely about what it's like to work in a magical preserve, and don't shy away from violence and death. The entire thing becomes a serious Crapsaccharine World.
The first book of the Dragons/Last Dragon Chronicles, The Fire Within, is massively strange in comparison with the rest of the books in the series. Although the book is set in Massachusetts, the characters talk in a very British manner (probably due to the author being a Brit), the main antagonist is Henry Bacon (who is a grumpy good guy in every other book), and book has a very simple and lighthearted plot about trying to save a one-eyed squirrel from a crow—with some Reality Warping thrown in. The rest of the series, however, is a dark, heady series about mankind's destiny, human nature and the nature of God, quantum physics, and what can only be described as the dissolution of reality at the hands of a group of superbeings. On the side, it also addresses issues like the nature of adultery and the ways in which we cope with grief. The author eventually started a spin-off series that was much closer to the original book, presumably to avoid warping the innocence of children further.
In the Nick Velvet stories by Edward D Hoch, Nick was originally billed as a 'Thief of the Unusual' rather than a 'Thief of the Worthless'. Several early stories feature him stealing items that definitely have a monetary value. The first story has him stealing a rare tiger from a zoo. It was several stories into the series before Hoch settled on the only stealing items with no value aspect that made the character unique.
Storm Front, the first book ofThe Dresden Files, matches the tone of the later installments fairly well, but refers to some world-building concepts that were changed in later entries of the series. For instance, there's a reference to vampires being unable to enter homes uninvited because they're creatures of the Nevernever, and need to expend constant effort to maintain corporeal form, and crossing a threshold uninvited blocks power. The threshold-blocking-power bit is maintained in later books, but vampires are later established to not be from the Nevernever, and only some breeds really have to worry about invitations. Also, there's a reference to a singular Queen of the Fae, while late installments establish two separate Fae courts, with three Queens each.
The second example, and a few similar cases, are justified in-series: Harry simply doesn't know this stuff until it comes up.
There's also the issue that in the early books, the author did not know the Chicago area very well, resulting in various errors in geography and architecture. This was remedied later after Butcher did his homework.
In Fool Moon, Harry summons the demon Chaunzaggaroth. His conversation with him makes it very clear that Chauncy is supposed to be a fire-and-brimstone Dante's Inferno demon, with it referring to Saint Patrick and the Catholic Church as "the other side." But in Death Masks he tells Murphy that "demons" are just harmful spirits from the Nevernever and that the Fallen which empower the Knights of the Blackened Denarius are the only true Biblical enemies-of-God demons that are active in the world.
Later books also establish that some regions of the Nevernever closely resemble the various underworlds of human myth, so it's possible that Chaunzaggaroth simply comes from a region that mimicsFire and Brimstone Hell, and deliberately milks that cliche in his conversation with Harry.
Really, the first three or even four books count as Early-Installment Weirdness. They focus almost exclusively on cases Harry takes in his job as a wizard-for-hire; a sort of magical Private Eye. In fact, that was meant to be the spirit of the books; a sort of Raymond Chandler meets JK Rowling. Elements like the Vampire Courts, the land of Faerie and the White Council were certainly there, but far in the background. Then book two added the Alphas, book three added the Knights of the Cross and expanded a bit on Harry's background, and book four added the Faerie Queens and the entire world therein, as well as expanding greatly on the White Council and its function in Harry's world. After that, Harry's work as a wizard-for-hire took a back seat to his war with the Vampire Courts, his ever-expanding supporting cast, the Fey and their influence in the real world, political intrigue and Manchurian-Candidate-style goings-on in the White Council, etc, all building on a previously barely-hinted at Myth Arc that directly led from book to book.
The chief differences are made manifest by watching the television adaptation of the books. The series was a loose adaptation to begin with, but went into production when only six books had been published, and heavily based their stories on the tone of the first three books. In the series, as with the first few books, the focus is on Harry as a special consultant to the Chicago Police, which is also true of the first few books, wherein he works with the police so often that he considers several of them to be his personal friends. Later, his only contact on the force is Lt. Karrin Murphy, who mostly is shown helping him with his problems rather than the other way around.
And after the aptly-named Changes, the stories shift yet again. Literally nothing is the same afterward, with the possible exception of the series still mostly taking place in Chicago, and keeps getting more different with each volume.
"Extricating Young Gussie", the first of P. G. Wodehouse's short stories containing Jeeves and Wooster. Bertie's personality and his relationship with Aunt Agatha are all in place, but their family name appears to be "Mannering-Phipps" instead of "Wooster". More noticeably, Jeeves appears for all intents and purposes to be an ordinary valet, and when Bertie gets in trouble and needs help, he has no idea who to ask. The surname "Wooster" and the personality of Jeeves as we know him today don't appear until the second story, aptly titled "Leave It to Jeeves".
Mercedes Lackey's Dragon Jousters series begins with a slave-boy raising a dragon. It ends with kings and the resurrection of a dead city and evil wizards. The first and the last book don't even seem like they're in the same series.
The early Goosebumps books could get surprisingly dark. They also didn't have every chapter end in a Cliffhanger as most of the books tend to.
Historia Brittonum, the earliest work offering an account of the supposed career of "King" Arthur. Only that Arthur isn't a king but a general; a certain Ambrosius is considered the most glorious king of the Britons instead; and there's no Merlin, no Sword in the Stone, no Guinevere, no Table Round, no Grail, no Excalibur, and no knights. There's essentially nothing of what defines Arthur in the writings of Chrétien de Troyes and Thomas Malory.
The first Gaunt's Ghosts book is near unrecognisable compared to the later ones. Instead of Loads and Loads of Characters, there's a handful of core cast and a bunch of Red Shirts. Instead of the Ghosts being an elite unit that take few casualties compared to other regiments, they die like flies. Instead of swift, dynamic battles, the first battle is trench warfare. note Indeed, when trench warfare reappears five books later, it's because of the incompetence of the local government and the Guard officers take every opportunity to note how bloody stupid and wasteful it is. Instead of the top brass ranging from decent to less-than-competent, the Ghosts' superiors are outright malicious and spiteful, along with an Inquisitor. Even a few Chaos Space Marines appear and are killed (relatively) easily, yet almost never appear in other books and when they do they're The Juggernaut. This is easily explained by how the Imperial Guard in Warhammer 40,000 originally were portrayed as helpless Cannon Fodder led by idiots and maniacs, but Gaunt's Ghosts transformed their perception and their portrayal into a genuine Badass Army.
Dave Barry's work in the 1980s was noticeably tamer, less biting, and less dependent on his myriad of Running Gags. It was around Dave Barry Slept Here that his Signature Style hit full steam.
His first four books also had illustrations by Jerry O'Brien. Most of the subsequent books had Jeff MacNelly (creator of the comic strips Shoe and Pluggers) until his 2000 death, when Gary Brookins replaced himnote also doing likewise on Shoe and Pluggers, although he actually took over the latter well before MacNelly's death. One of the exceptions was Slept Here, possibly because it had maps instead.
The first few installments of Uncle John's Bathroom Reader were much smaller (the first one was only 224 pages) and its articles were far shorter — usually a two-to-three page summary on a topic, followed by a bullet list of trivia. By Uncle John's Ultimate Bathroom Reader, the average size of the book more than doubled as the articles became longer and more in-depth. Eventually, the writers even started including multiple-part articles spread across the book, and an "Extended Sitting" section composed of double-length articles. Their research and copy-editing have also improved significantly.
The first book, having the burden of introducing the world of Classical Mythology to newcomers, goes to great lengths to point out that Greek Mythology is different from Christianity. These include scenes such as Percy being told not to worry too much about the possible existence of a "Capital-G god," and Percy commenting on seeing a televangelist in the Underworld (Annabeth tells him that the Mist probably makes him think he's in Hell). After the first book, Christianity is rarely (or not at all) mentioned.
Also, in the first book and parts of the second, Percy would usually refer to gods by family names, such as Percy calling Hades "Uncle." By the time the third book rolls around, this is almost completely dropped and gods are treated with much more respect, normally being called Lord or some other official title.
A Song of Ice and Fire: Tyrion is subject to early installment weirdness. In the first book he's capable of some impressive acrobatics which seem fairly unlikely given the cramps and such described later on. Apparently this was due to Martin's early plans for Tyrion being somewhat different, but it gets a reference in A Dance With Dragons when it is revealed that his uncle Gerion taught him some tumbling tricks.
The four Wardens (of the four cardinal directions) seem early on to be very important positions, with Ned objecting to Jaime Lannister being named Warden of the East (because he will eventually inherit his father's place as Warden of the West as well). Later on this seems to be not much more than a title, with the lords' power determined by their family and alliances, and it seems that Jaime, as one of the Kingsguard, is barred from holding such a title anyway.
In the earlier half of the first book of Robert Jordan's The Wheel of Time, the young central characters from the Two Rivers, particularly Rand and Mat, are depicted sheepishly performing chores for the adults in order to be given a treat, and playing pranks that are on the level of a five year old. Not to mention they all live with their parents. You could be forgiven for thinking they're each about 13 at the oldest, but if you actually take the time to do the math, you realize they're actually supposed to be around twenty. By the time we get to the end of the first book, Jordan seems to have gotten a better grip on how legal adults in a medieval equivalent setting are supposed to behave. They never really outgrow their prudishness, but compared to their initial depiction, their behavior becomes far more adult-like later on.
The short story, Weyr Search, that became the opening of Dragonflight and launched the Dragonriders of Pern series, has a number of differences from the rest of the book (written years later), and the book has marked differences from the rest of the series. The biggest oddity of Weyr Search is that Lessa has an explicit projective empathic ability that works on humans; she uses it on F'lar. Of note from the book to later novels, the dragons aren't given actual lines — the narration paraphrases their speech to their riders (as with fire lizards later), making it seem more empathic and less explicitly telepathic.
The naming conventions of Dragonriders changes between the first book and the rest of the series. In Dragonflight, Lessa and F'lar discuss a newborn baby whose name has the familiar "consonant-apostrophe-three letters" combo. In later books, it's established that male Weyrfolk are given a name that's a combination of the mother's and the father's name, which is changed to a shortened version if they become Dragonriders. For example, in Masterharper of Pern, young F'lar is called Fallarnon.
The Warrior Cats series has several, especially in the first book:
Each Clan keeps mostly to itself and doesn't know much about what's going on elsewhere in the forest, and the other Clans' territories are generally a mystery to them. Tigerclaw freaks out in the first book when they take Yellowfang as a prisoner because he thinks that now ShadowClan will know where the ThunderClan camp is, and that they'll need to move, while in later books (even ones that take place around the same timeframe) they actually visit each other's camps on a fairly regular basis. Likewise, in the first book, they say a few times that "that cat must have been killed by an enemy patrol" and just forget about it - most notably the ShadowClan leader's death - when later on such an event would be huge news and they would actually confront the other Clan and try to figure out what happened. This is probably partly because since the first book they've established exact rules for the previously-vague warrior code, one of which forbids killing except for rare circumstances.
Their terminology changes a bit, such as the way they use hyphens and capitalizations in words (i.e. "Clan mate" becomes "Clanmate"). Also, in the first book they use the word "queen" for any female cat, but later on it only gets used for females currently pregnant or nursing kits, and "she-cat" becomes the general word for "female".
The Clans are a lot more formal early on; cats refer to parents by their actual names rather than calling them "mother" or "father", and there is almost no use of slang such as "cool". The Gatherings in the first series tended to be different groups of cats mixing and talking about current events - for example, a senior warrior talking to a group of apprentices, or a young warrior joining a bunch of elders and medicine cats in a discussion, while lately it's mostly cats sticking with their own age group and gossiping.
Mates aren't, for the most part, treated as major relationships in the first series, and it is mentioned that warrior fathers don't stay close to their kits (with one or two rare exceptions). In the third series, one cat who had kits as the result of a one-night stand (which in and of itself is rare later on) is critisized because he doesn't want to play with his kits, and in the third and fourth series especially, everyone gossips about young couples and young cats talk about who they like.
Early books in Sword of Truth are much more stock fantasies. The most common criticism of the early books was that Goodkind was ripping off The Wheel of Time. It's not until the fourth book that Goodkind began adding his Objectivist philosophy and Author Filibusters, and the series took a much different direction.
The Horatio Hornblower books are written in Anachronic Order. Lieutenant Hornblower, published seventh, is the story of how Bush met the title character when they were both young lieutenants. This retcons The Happy Return, published first, where Bush apparently met Captain Hornblower for the first time at the start of the Lydia's voyage.
In the third novel, Sojourn, of The Dark Elf Trilogy, we have Bruenor Battlehamer's constant desire to eat Roddy McGristle's dog. We're never given a reason why he wants to, he just... wants to eat dog-meat. It's not even implied that this is something normal for dwarves in the setting. At the story's end, he gets to enjoy a roast dog's leg. Ironically, that he never thinks this way again is actually justified; after he finally gets to eat the roast dog meat, he is quite horribly sick, vowing he'll never eat dog again.
Arly Hanks has a deputy working for her in the first of Joan Hess's Maggody mysteries, and the sheriff's office largely takes over the investigation into Jaylee's death, in contrast to later books when she has no underlings and is railroaded into do all the grunt-work because Sheriff Dorfer is out fishing or watching baseball. Mrs. Jim Bob actually chews out her husband for hassling Arly, rather than sniping at her in Holier Than Thou fashion, and Jim Bob himself seems genuinely fond of fishing and hunting, rather than using them as a cover for his philandering.
The Rainbow Magic series has this. The first series of books took a while to establish Kirsty and Rachel before sending them to Fairyland, the goblins were built up as major threats, they had to find the fairies themselves rather than magical items, and Jack Frost was captured at the end and nearly melted until the fairies relented.
It was also very clearly meant to be a standalone series. The Weather Fairies series was only made due to its popularity.
The Tortall Universe has been subject to some Continuity Drift. In the first quartet, the narrative departs from Alanna's POV far oftener than the subsequent series (we've hardly ever seen the villain's POV again). She also tangles with demonic entities and "elementals" which so far haven't shown up again, although the Ysandir did get a namecheck in the Provost's Dog trilogy.