Mallory: What year do you think this is?!An ambiguous time period is where the series takes place at a certain time in the past or future and in the same universe as ours, except for the story elements added by the author, but doesn't state anything specific. This is either because the time period is completely unmentioned, or because it's mentioned but elements of the story or Word of God state that the fiction uses a different calendar than ours. Sometimes Anachronism Stew will unintentionally (and sometimes intentionally) confuse viewers into wondering when the work takes place. When the ambiguous time period is obviously not long ago, it's an example of Present Day Past. Could also be an unofficial form of a Retro Universe. This trope is the temporal version of Where the Hell Is Springfield? Contrast Period Piece and Unintentional Period Piece.
Archer: I... yeah. Exactly. Good question.
Archer: I... yeah. Exactly. Good question.
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Anime and Manga
- Gundam takes place in the future, but thanks to their excessive use of Alternate Calendar (several, in fact) how far in the future is impossible to pinpoint.
- Although we do get a few clues. In Mobile Suit Gundam 0080: War in the Pocket it's mentioned January 14th, U.C. 0080 falls on a Monday, while Mobile Suit Gundam ZZ mentions 0088 is a leap year. Apparently somebody once did the math based on this and found 2047 to be the earliest possible date for the changeover (technically, the earliest date would be 2019. The 2047 start date much touted in Fanon is based on some sourcebooks that give 2045 as the last AD date mentioned but don't specify when exactly the switch happened. Sunrise has since declared all timelines that mention the AD era non-canon, though, so now it's anybody's guess).
- Gundam Wing seems to take place in the mid- to late 23rd century, based off of two pieces of information: the novelization of the series mentions that the circus where Trowa Barton hides out is about to celebrate its 600th anniversary, and the circus' logo (seen in artbooks) has "Since 1667" written on it.
- Inazuma Eleven seems to take place some time in the present to its release, however in the follow up, Inazuma Eleven GO which takes place 10 years later, the technology is still how it would be in 2008. This is especially jarring whenever you see a character use a cell phone, the show's cast using cell phones actually being the theme of one of the show's endings. And they're all using flip-phones you'd expect to find in 2005.
- It's hard to pin when Michiko & Hatchin takes place. There are vehicles from the 1970s, TV broadcasts with an '80s and '90s style, and every building and infrastructure looks run-down.
- It's not made clear when most of the Angel Beats! cast died. It's implied that you don't have to all be from the same time period in order for them to be together, nor do you have to be a school kid to appear in Heaven (you automatically just de-age into your younger form). Kanade received Otonashi's heart after he died but it's unknown how long she lasted with it. If she died decades later, the anime could take place 20 Minutes into the Future. On the flip side, Ayato's school uniform (a gakuran and a hat) is outdated by 21st century standards. This implies that he either died decades earlier or that he was an adult when he died.
- Professor Gerald's diary in Sonic X is signed "20XX". The diary is around 50 years old.
- It's hard to tell when exactly My Hero Academia takes place, other than it being in the future. Though the level of technological advancement shown seems to place the setting 20 Minutes into the Future, it's been stated that most scientific research has slowed down in order to focus more on the study of Quirks, meaning that the actual year could be centuries ahead of ours.
Film — Animation
- Disney Animated Canon:
- The Lion King gives no indication of what time the story takes place. There are references that hint it is set in present day and the cartoon series confirms this, however it's very dubiously canon. On the other hand, since we never see any humans, it's still plausible to depict the setting as taking place in very ancient or even prehistoric times.
- A lot of the Disney films have this; being fairy tales, they're just set "a long time ago." Sleeping Beauty actually does say "This is the fourteenth century" (though the fashion doesn't match) and newer films tend to aim for more historical accuracy (for example Frozen is set in the 1840s, albeit with some Anachronism Stew here and there), but most of the rest don't even have that.
- The Incredibles seems to take place in 1960s, but they have computers that function similarily to what we have today. Even the one seen in Bob's office, despite it's retro design, would be out of place for that time period.
- There's also VHS players, which didn't come out until late 70s.
- Brad Bird says that the time period is based more on what people in the '50s and '60s thought the future would be like.
- Further complicating things, the comics have cell phones and Internet, in line with late Noughties' technology (Violet has her own laptop, for instance).
- The Peanuts Movie is deliberately vague about when it is taking place, aiming for both nostalgia and sense of timelessness that could (with a few exceptions) pass for any era between the 1940s and today. Among the older elements are Snoopy still using a typewriter (rare since the 1990s at the very latest), Linus still referring to World War I as "The Great War", Westerns still being popular (The Lone Ranger is evoked), and interest in the 1960s space program. Accompanying those are more modern or contemporary tropes, such as karate and 21st-century dance pop (which may or may not be perceptible to the characters).
- When Marnie Was There lacks much modern technology and everyone has timeless modern day attire. It could easily take place in the 90s, 2000s, or 2010s. Marnie makes it even more confusing as her clothes and name are old-fashioned, though it's justified as she's Dead All Along and from the mid-20th century. An easily missed scene shows a character with a smartphone, implying the movie takes place in the 2010s.
- The Madagascar franchise does not make it especially clear when it is set, featuring a somewhat retro aesthetic but dates visible from Freeze-Frame Bonus in multiple movies go back and forth between implying the 80s and implying present day and given that realistic animal ages are used, there can't be that much time between movies.
Film — Live Action
- Batman loves this trope. Reporters use very old fashioned cameras and a lot of the film's elements seem to be from The '40s, and yet Batman himself has very modern technology; far better than anything that existed when the movie was made! The closest the franchise comes to explicitly addressing this is in the 1989 original, when a character is shown reading a newspaper from 1947 - but the scene is also set in a newspaper office, where archived newspapers are certainly not uncommon. The costume designers for the Burton/Schumacher films even admitted that, as least as far as the costumes are concerned, the second film, Batman Returns, is basically set in an alternate 1947 with modern/futuristic technology.
- The Wizard of Oz could take place in 1899 (when its source material was written) just as easily as it could in 1939 (at least in Oz, where the Emerald City's technology is state-of-the art by 1930s standards and the skirts on the women are shorter than the 1890s would have allowed). The simple costumes, rural setting, and old technology (including a horse-drawn carriage) are all pretty vague. Miss Gulch's outfit in particular evokes more of a turn-of-the-century appearance. Of course, it helps that the state of Kansas (except for Kansas City, of course) is even in the 21st century a fairly sleepy place where things tend to stay the same.
- DodgeBall: A True Underdog Story: Word of God has it that the movie was supposed to take place in the early 1990s, but a number of thing (including Peter renting Mona Lisa Smile on DVD, as well as the existence of digital cable) would suggest it's just in the present day; it pretty much looks as if it could have been set in the present day.
- Most of the time, The New Adventures of Pippi Longstocking seems to be set around the 1940s (when the first books were written). However, the characters are shocked when a local man "invents" a flying machine and Pippi's sailing adventures with her father seem to be out of the 17th century.
- 10,000 BC appears to be set in prehistoric times, with the main character encountering both a wooly mammoth and a saber tooth tiger. However, he ends up somewhere that appears to be ancient Egypt or at least Mesopotamia (an emperor is having a large pyramid built). Based on the hints in the story, the civilization is meant to be an Atlantis-like place that gets destroyed in the events of the movie, but inspires the later, historical civilizations.
- Brazil is set "Somewhere In The Twentieth Century"- whilst genre convention would normally dictate a dystopia of this type, it's also very Zeerusty and could just as easily be a twisted version of the then present-day world. It's left deliberately ambiguous, and in a way the precise setting isn't meant to be that important.
- It is hard to pinpoint exactly when Final Girl is supposed to be set. The cars and the dresses the women wear all point out to The '50s, but the television in William and Veronica’s motel room is in color with a digital display and the guns they use are far more modern than that.
- A Girl Walks Home Alone at Night: Each character seems to exemplify a different time period in their clothing and demeanor: The Girl, in her striped shirt, short hair, and love of records, seems '60s, Arash loves his '50s clothes and car, Atti looks like she walked out of the 1930s, etc. The actual set looks modern, with oil drills and powerplants in the background.
- The 1993 film adaptation of The Fugitive plays with this, and not just because it's an updating of a 1960s TV series. The movie does a very good job of not tying the story to any particular time period, partly because the early 1990s (the filming date of The Fugitive and ostensibly its time period) was a fairly conservative era with very few particularly glaring fads or peculiarities and partly because a few subtle retro touches are slipped in, such as a Slavic immigrant who can barely speak English and The Dragon of the evil plot being made up to look like a grotesque Film Noir villain. The most specific technology the movie ever calls attention to is computers - specifically, PCs with MS/DOS screens and dot-matrix printers, apparently putting the action sometime between 1980 and 1995.
- Shakes the Clown: The city of Palookaville appears to be stuck at some blurry point between the 1940s and 1960s, with certain characters in suits and fedoras and clowns still hosting children's TV shows - if not for references to Madonna and the Watergate scandal, and cocaine being a recreational drug.
- It Follows appears to take place in a world that is a strange blend of various decades between the 1950s and 2010s. The TVs are 70s at least, and play old black-and-white 50s features too often for it to be any sort of marathon or simple showing of classic movies. The cars are largely 60s designs. Our heroine visits a very retro movie theater with a live pianist. One of the main characters reads a book on a strange contraption roughly resembling a Kindle in the shape of a flip-mirror. Cell phones are ubiquitous. Not to mention the strange lack of black people in Detroit.
- Noah is set at some time in the remote past (barring the possibility that what we're seeing is a post-apocalyptic wasteland, of course), but we're not told exactly when. The only compelling clue The Bible offers is that it's definitely taking place before the reign of King David (circa 1000 B.C.); beyond that things get very vague. And given the characters' tribal/hunter-gatherer lifestyle and the fact that agriculture barely exists, it's obviously happening before 3000 B.C. Finally, one animal seen fleetingly in the film appears to be some bizarre prehistoric creature, suggesting that the action is taking place at least several thousand years before the rise of human civilization. So this could be sometime during the late Paleolithic Era, perhaps a few centuries or so before the Western Hemisphere was settled, resulting in a date of, say, 14,000 B.C. (Of course, Jewish tradition - where the story of Noah began in the first place - directly contradicts all of this by holding that the universe was created no earlier than 6,004 years ago.)
- Rob Zombie's 2007 reimagening of Halloween did this on purpose. The early scenes of the movie take place 17 years before the rest of the film, but they don't necessarily depict 1990. The fashions, cars, etc are actually mostly (but not totally) 70s-influenced. However, the present day scenes mix in some 90s technology such as cell phones with (then) contemporary fashion and cars.
- The London scenes of the earlier Harry Potter films are mostly set in areas of old buildings, so time period can be hard for an average moviegoer to determine, the main clues of then-modern times being the cars shown. A brief appearance of the now-demolished Southwark Towers, however, narrows down the possibilities to between 1976 and 2008. Averted by the books, which explicitly take place between 1991 and 1998.
- The Roald Dahl book The BFG was released and set in the 1980s, as shown by the Queen being fairly young and brown-haired then. In the film by Steven Spielberg, the cars seen are rather old-fashioned but the Queen is much older and looks like her present day self. Adding to the date clouding is a scene where she calls "Nancy" on the phone and asks if "Ronald" is there.
- In the 2008 film Penelope, not only do cell/ mobile phones and the internet apparently not exist, it's questionable whether answering machines even exist given the fact that several characters are shown surrounded by tons of phones. Notably, said phones are all corded, and Penelope has no trouble finding pay phones to use. Something of a plot point is made of Penelope's dowry, a practice no longer in play in modern-day America (at least officially, though there might still be some cases of a form of Nobility Marries Money quietly happening). The clothing, however, is distinctly 1990s/2000s, credit card useage is apparently common, and things such as shatterproof glass exist.
- Robert E. Howard's Conan the Barbarian stories take place sometime between 20,000 B.C. and 9500 B.C. Or as his short story "The Phoenix on the Sword" puts it, "Between the years when the oceans drank Atlantis and the gleaming cities, and the years of the rise of the Sons of Aryas."
- Warrior Cats appears to take place in the present day. However, nobody knows how long in the "past" the background lore goes back - Word of God has flip-flopped on whether the Clans have been in the forest for 50 years or 30 years, both of which are considered to be too short by fans considering all the leaders and generation gaps we know about. When you go all the way back - before the Clans were formed, before the Tribe was formed, back when their ancestors lived by the lake - there seems to be modern construction equipment; it describes yellow vehicles. Most people accept the series as taking place slightly in the future because of this, but it's not clear exactly when.
- In Maggie Stiefvater's The Scorpio Races, the time period is never mentioned. Word of God has said that she knows when it is set, and the location of the island it's set on, but she will not say.
- Based on the hints, The Quantum Thief seems to take place approximately 300-400 years to the future, but time has become almost irrelevant in a world where most human beings have been uploaded into immortal computer systems that can alter their subjective sense of time by increasing or decreasing processing cycles. The oldest Sobornost Gogols that work in the Deep Time are believed to be at least tens of thousands of subjective years old.
- It's hard to nail down exactly what period A Series of Unfortunate Events is set in, as "advanced" computers lie alongside telegrams and early mid-19th century automobiles and fashions, as well as practically medieval outlooks on child labour, medicine and the law.
- It's hard to pinpoint exactly when the stories featuring The Berenstain Bears are taking place. The action never leaves Bear Country, which features very few technologies aside from (early-to-mid-century) cars note and (pre-1950s) telephones. Shopping malls and color television appear to be fairly new, suggesting an approximate date of 1970; however, one book shows what looks suspiciously like a Rubik's Cube, which was invented around 1980.
- Diamond Brothers series became this, due to the series schedule slipping a lot. The first book The Falcon's Malteser was released in 1986, so one would think that the series would continue to take place during the 1980s, but then as the books were slowly released, they began to suffer from Time Marches On once the fourth book was released the 2000s. Then when the recent book was released in 2007, one of the brothers had turned an age. It's an '80s/'90s/New Millenium mishmash.
- It would be easy to assume that Charlie and the Chocolate Factory takes place in the 1900s or 1910s (around the time of the author's childhood) because of the Bucket family's absurdly exaggerated poverty and Charlie's father's horrible factory job, except that Mike Teavee is considered a Spoiled Brat because he's addicted to television. The sequel confuses the issue even more with all its science fiction elements while being an Immediate Sequel.
- Pryor's Place falls victim to this: the basic format of the show is Richard Pryor reminiscing about various childhood experiences, however his stories show his childhood friends in obviously 80s attire, not to mention such things as break dancing and arcades exist. It could all be justified, however, in that his stories are fictionalized versions of his life.
- The U.N.I.T. stories in classic Doctor Who take place sometime in The '70s, or Is it The '80s? Not even The Doctor knows for sure. Not even UNIT itself knows for sure.
- Similar to the above-mentioned Batman and the below-mentioned Batman: The Animated Series, Gotham's version of its title city has tons of Anachronism Stew going on; the many retro touches include 1950s (and in some cases older!) music still being popular, mild disapproval (from other gangsters) of a woman wielding great power in the underworld, and Oswald Cobblepot's Ambiguously Jewish immigrant mother. Cell phones seem to phase in and out of existence as well, with Bruce and Selina scouring downtown Gotham for a phone booth in a season 1 episode. The intent seems to be that Bruce Wayne is Batman in The Present Day, therefore this is The Past, but making it clear when in the past would tie down how long it's going to take Bruce to become Batman. note
- In the early episodes of Star Trek: The Original Series, the writers deliberately avoided mentioning the exact time period the show takes place relative to the present day, but by the time of episodes like "Space Seed" (which involved a group of Human Popsicle superhuman exiles from 1996) it's established the show takes place in the mid-23rd century.
- Legion has 60s/70s fashions and aesthetics, as well as dialogue implying it takes place in that period, but this is contrasted with modern and at times futuristic technology.
- On Riverdale, an adaptation of Archie Comics, there are laptops, but old style cars are commonplace. A local gang are referred to as "greasers", and Jughead dresses in an emo style rooted in The '90s. The football uniforms look largely dated, but the students use modern slang, and attitudes towards sexuality and race are modern as well. The dialogue even explicitly states that the timeline takes place in the present day. The Season 2 premiere featured the Riverdale General Hospital, with doctors and nurses wearing 1950's style uniforms. Really, it's a healthy mix of the The '50s and the 2010s. Lampshaded when the drive-in is torn down because the times have changed.
- Pushing Daisies has a lot of homes with older television sets and Parisian-style phones, but with very few references to the Internet.
- A Series of Unfortunate Events, which, like the above, had Barry Sonnenfeld as one one of its directors and producers, is this in spades. But some references to online auctions are used as a joke (in particular, in the first episode when Count Olaf is referring to a defective hourglass).
- The Good Place, in season 2, after many years spent rebootingnote , celestial beings still make reference to pop culture of the late 2010s. It's possible that time works differently in the afterlife.
- The Far Side tries to avoid pop-culture humor in favor of animal or science jokes and generic satire, with the human characters dressing as if it's some point between the 1930s and the '60s. Adding to the confusion are the "historical" strips set in the Stone Age, medieval times, the Old West or whatever, which are sometimes described in the present tense and sometimes in the (implied) past tense.
- In Paranoia the year is always 214 since Friend Computer likes the number. This means that the players have no idea how long Alpha Complex has been a hellhole.
- Monopoly would obviously have to be taking place sometime before about 1890, when monopolies were declared illegal. However, the drawings on the board and the cards are 1930s style, and one of the playing pieces is a sporty roadster.
- The Rocky Horror Show left the time period unspecified, but the movie has Brad and Janet listening to Richard Nixon's resignation on the radio which would set it in 1974.
- Double Dragon 2 places the game in "19XX".
- EarthBound takes place in "199X". Its sequel is even less helpful.
- Nigel from The Lost Crown never does get a straight answer when he asks what year is it in Saxton, a region filled with anachronisms due to its numerous hauntings.
- Live A Live avoids specifying dates at which chapters occur (although the timeframes are much clearer). Logs in the Science Fiction chapter even go so far as to hide dates with X's (although the "copyright" text in the Captain Square minigame makes it clear it takes place no earlier than 22nd century).
- The kids at Whispering Rock Summer Camp in Psychonauts talk and act like relatively modern-day kids, but they make references to media and cultural phenomenon from all over the place. The fact that they're all psychic and can, therefore, see things in the future and past, only serves to make it more ambiguous. And if you thought the surprisingly-detailed timeline of Whispering Rock's history you can read in the parking lot will help you, trust us, it won't.
- The Famicom in Madotsuki's room suggests that Yume Nikki takes place at least as far back as The '80s (though one of the dream worlds is a clear homage to EarthBound Beginnings, which was released in Japan in 1989), but it could otherwise be set anywhere between then and the Turn of the Millennium (when the game was made). Just one of the many ambiguous details this setting has to offer.
- It's natural to assume that Far Cry 2 takes place in the same year it was released (2008), and no specific date is ever given, however you never see any technology that wasn't around in the 1980's or 1990's (one character, a Western journalist, even uses cassette tape recorders and a black-and-white film camera). The ending also implies the game is a flashback that takes place at some point prior to the present day. A character in Far Cry 4 (which takes place in 2014) is heavily implied to be one of the villains from Far Cry 2 who has undergone a Heel–Face Turn; he looks at least a couple decades older than the character in Far Cry 2 did. Given that the game is loosely based on the Sierra Leone civil war of the 1990's, this timeframe makes sense.
- As a possible reference to EarthBound, Undertale takes place in 201X. Or rather, the opening scene takes place then; the actual events of the game take place later — implied to be much later. Yet the human world looks more or less in the current day, and technology sometimes seems to be a bit outdated, like the designs of the cellphones and computers.
- Five Nights at Freddy's:
- Five Nights at Freddy's 4 unambiguously takes place in The '80s, before the events of the first game, but beyond that, it's unclear as to just what year it takes place in. At first, it would appear to be 1987 due to the teasers prior to the game's release featuring the number, toys of the Toy animatronics from the second game (which happens in '87) appearing, and the entire game building up to what looks like the Bite of 87. However, an Easter Egg reveals a TV advert/program that has a copyright date of 1983 — this, along with Fredbear having a restaurant open (when by 1987 it had been closed for years) seemingly suggests it happens on that year instead. Then the Halloween update added Nightmare BB (whom Scott considered canon unlike the other new animatronics), who looks like his Toy bretheren, seemingly putting it in 1987... only for Sister Location to have an Easter Egg involving the rooms from 4 appearing by typing "1983" on a keypad in the Private Room.
- Five Nights at Freddy's: Sister Location takes place after Freddy Fazbear's Pizza closed down, but due to its numerous iterations, it's hard to say which one specifically it refers to. The presence of high tech animatronics and even an A.I. guiding the player, as well as a voiceover from who is implied to be the Greater-Scope Villain suggests it happens in between the first and third games (thus the mid/late 1990s to the early 2020s), though the exact year is still unclear.
- It's difficult to read exactly when the Devil May Cry series takes place. The models of the cars and Dante's rotary phone imply that it must be the 50s or 60s, but then Dante's boombox (right next to a jukebox, mind you) means that it must be at least the late 60s, then Nero shows up with some very modernized-looking cordless headphones and it really becomes impossible to determine the time period.
- Grand Theft Auto 2 is set in an impossible time with contradictory hints or statements. The introductory video was filmed in late 90's New York City and looks nothing like the game. The game itself is set in "Anywhere City" where several factions vying for control of the criminal underground, the largest being a company called Zaibatsu Pharmaceuticals. The city is generally has a Cyberpunk Used Future look to it, and the cars are designed with a retro-futuristic look ranging from 30's to 70's style vehicles, and including styles from America, Europe, and even Soviet Europe (exclusive to The Mafiya). More specific clues are:
- The leader of the Russian Mafiya is a former Red Army Soldier, implying it takes place within a lifetime of the dissolution of the Soviet Union.
- Promotional material for the game lists it as "3 weeks into the future", and a promotional website also references police records from 2013.
- A DJ on the radio mentions the new millennium is coming, which would put it just before 2000 or just before 3000.
- Strikers 1945 is specifically set in 1945 (the first game anyway). The planes/tanks resemble those from the World War II era, but they all have futuristic weapons, and the bosses are giant transforming war machines.
- Word of God states that the calendar saying that the year is 3031 in Ava's Demon is not the BCE/CE calendar we're familiar with.
- Alice and the Nightmare is rather ambiguous about its period. One one hand, the fashion is victorian and there are carriages used; on the other, there are also mini-fridges, plasma screens and Tron-like suits. The closest we get to a clue is Alice and Edith both reading Lewis Carrol's book.
- It isn't really clear at what time minus takes place. Background characters often dress like people in the 1890s, but none of the main characters do, and people's attitudes don't seem to be any different from the modern day. It is implied that mid-20th century technology, including automobiles, exists, and city skylines are dominated by modern-looking skyscrapers, but we never see cell phones or even computers. Finally, when one character is sent to the past, she is stuck in what is very clearly Victorian times, yet is able to live long enough to return to the present, albeit as an old woman. Word of God says the comic was designed as a throwback to the old early 1900s newspaper strips, and so the setting could be anywhere between then and the late 2000s, when the comic was made.
- A Running Gag in Archer is the Anachronism Stew, which is lampshaded often. "No Good Deed" shows a gravestone that states the series takes place in the 1900s, but flowers cover up the last two digits. Word of God has stated that it is pretty much a mix between 1960s decor, 1970s cars, and early 1980s computers alongside modern cell phones, the Internet and morals.
- Batman: The Animated Series has tons of Anachronism Stew and the few dates shown contradict each othernote .
- Hanna-Barbera's series of The Little Rascals is supposedly set in the late 1930s, but they have microcomputers, commercial television and push-button traffic controls.
- Rugrats could easily be mistaken for perpetually taking place in the early 1990s - especially since the successor series, All Grown Up!, takes place ten years later and was created after the Turn of the Millennium - but later episodes imply the late 1990s due to the Internet playing a large role in the second movie's plot.
- Ed, Edd n Eddy was created with this in mind so it can appeal to a varying amount of age groups. The series could take place in The Noughties just as easily as it could take place in The '70s. Small references here and there, especially in later seasons, heavily imply that it takes place in the 2000s, though. The fact that it crossed over with Codename: Kids Next Door and The Grim Adventures of Billy & Mandy further imply it taking place in the 2000s.
- The Amazing World of Gumball. Most of the appliances have a very 70's/80's aesthetic (and have a lot of inventions from that time, like VHS tapes and video rental stores), but there are a lot of late 20th/early 21st century inventions, like DVD players, social media websites (Elmore Plus, which is a mix between Google Plus and Facebook), a YouTube equivalent website (Stream It), and in "The Refund," Darwin says "Why is it called [the Ripley] 2000 anyway? It's not like it's the future anymore!" One of the writers has stated that he can't remember if the series takes place in 1950, 1985, 2012, or 2098. Also, sentient AIs are a commonplace occurrence, and dinosaurs haven't gone extinct yet.
- The Simpsons achieves this largely by virtue of being a Long Runner where the characters are Not Allowed to Grow Up — the earlier seasons in particular had deliberate elements of Retro Universe, but the show has been on so long and is such a venerable property that the established continuity often doesn't fit with the generally present-day setting. So, for example, flashbacks to Marge and Homer's high school days are still set in The '70s (except for one widely-disliked episode that had them as college students in The '90s) but flashbacks with Bart and Lisa as little kids are generally set in the Present Day Past — although earlier episodes established their birth years as 1980 and 1984 respectively ("present day" Bart and Lisa are ten and eight, so that gap doesn't make sense either). It's probably best not to think too hard about it.