Any event of the Society for Creative Anachronism, where you can see examples of everything from 16th-century German armor to Moors to Vikings to Romans to Samurai all competing in the same tournament, or a Viking chatting with an Elizabethan lady over a display of Catholic prayer beads. Largely a result of the basic structure of the organization; anything before 1600 AD is fair game for re-enactment. Individuals will generally be faithful to a period in their dress, though this also varies.And they merrily lampshade it themselves, as in Our Kind II: Mistress Laurel Seamchecker Explains It All At You, in which a character explains that "Historically, clothing is divided into three periods: bearskins, funny clothes, and modern."
Medieval Re-enactors in the UK used to annually attend the Battle of Tewkesbury each year, but until recently, it was well-known for allowing anyone with vaguely medieval kit (garb to SCA types) onto the field. At one of the last events before it changed to a more authenticity based re-enactment, it wasn't uncommon to see 9th century Vikings, the (ubiquitous) kilted Scotsmen and Normans from 1066 fighting against bill blocks.
Renaissance festivals in general are often actually more of a pastiche of Middle Ages, Renaissance, and Fantasy (including fairies, etc.).
Camlann Medieval Village, outside Seattle, does an admirable job of being as authentic as possible. Unfortunately, drive for authenticity doesn't exempt them from liquor laws, fire codes, or health regulations — forcing them to institute smoke detectors, ID checks, and plastic take home containers.
Cowboy Action Shooters love this trope. While participants are encouraged to wear appropriate costume, there is no rule forbidding (for example) a Confederate soldier from using an M1887 Winchester shotgun. Part of this is because the governing organization permits and encourages Western movies to be used as inspiration, and classic Westerns are notorious for this trope.
During the 2008 campaign, then-Senator Joe Biden, famous for his folksy gaffes, said "Now, when this country entered the Great Depression, our president, Franklin Roosevelt, went on television and spoke of how to get this country out of it." The Daily Show had a lot of fun with this, since 1) Herbert Hoover, not Roosevelt was President at the time, and 2) Television barely existed at that time. (In Biden's defense, Roosevelt was the one who got the world out of the Depression, which he inherited as President, and spoke on the radio to the public in what would become known as his Fireside Chats, so Biden wasn't entirely off base.)
Al Gore stated in an interview that he grew up reading The Very Hungry Caterpillar as a kid. The book was written and first published in 1970, a year after Gore graduated from university.
Modern printings of Old English works gleefully use the letter 'W', which would not be created for a few hundred years; however, the only other option would be to use the contemporary letter wynn ('Ƿ'), which was abandoned due to constant confusion of it and 'P'.
People's memories can be this way. Some people being interviewed about their experiences surviving the great Johnstown Flood of 1889 years after it happened mentioned that they checked their wristwatch - even though wristwatches didn't become popular until the 1920's, 30 years later. Their memories could have melded it with the similar (but less well-known) Johnstown Flood of 1936.
Sam Wineburg's Historical Thinking and Other Unnatural Acts argues that most of us see time as a sort of dual choice: the present and "the past," which includes everything from cavemen to toga-wearing Romans to medieval kings and knights to Elvis Presley, and that it's really a fairly unnatural (and therefore difficult) act to periodize the past and think of it as a flowing narrative rather than a list of events. In fact, most people up until relatively (in a historical sense) recently wouldn't think of history any other way. If you told that Medieval artist in the opening of this topic that he was wrong in painting Jesus in Medieval Italian attire, he would just scratch his head and look at you with a puzzled expression.
This happened, after a fashion, at various times in history when much more technologically advanced civilizations came into contact with isolated and more rural civilizations. Europeans settling the Americas, the late Edo and early Meiji Periods of Japan, WWII cargo cults, and so on. The previously isolated civilization incorporates technology that is effectively decades or even centuries ahead of what they had before into their lifestyle.
This still happens as parts of the world that are considered "third world" skip several generations of technological advancement. Cell/smartphones are the quintessential example: instead of stringing copper to do landlines first, many places without any telephone service now simply start with wireless, this leading to scenes where a Masai cattle herder, otherwise looking very traditionally dressed, hauls out his Nokia to answer a text.
This can be seen in America with the Amish who use some types of modern technologies alongside a mostly agrarian lifestyle more typical of the early 20th century than the early 21st.
In the Canadian Arctic, one can still find people who use a dog team to go hunting. Use of the dog team goes back thousands of years, the sled probably uses metal and plastic, the rifle might be a century-old design, and there's good odds they're carrying a GPS and/or satellite phone. This is often because the traditional way of doing things still has a lot of advantages over the newer methods; for instance A dog sled is better suited to snowy terrain than most vehicles and the acute senses and natural pathfinding abilities of the sled dogs can be invaluable. There are documented cases of sled dogs instinctively dragging their master back to civilization after he became sick or injured, saving his lifenote and, in a pinch, you can eat the dogs, as Roald Amundsen did on his trek to the South Pole.
During World War I, trench warfare and rapid-firing machine guns brought back many artifacts of war that had been rendered obsolete decades or centuries before, such as metal helmets (the Commonwealth forces based their common soldiers' on the ones of English Medieval archers; machine gun crews adopted others closer to knights), maces, hand grenades, pavise-style shields (for sharpshooters) and chain mail and plate armor for assault troops. The advent of bomber planes and tanks made trench warfare obsolete in turn, and put an end in consequence to most of these 'revivals'.
The Pre-Columbian American cultures, developed in complete isolation from Eurasian cultures, are often this when looked at from a Eurasian-centric perspective. People in Mesoamerica at the beginning of the 16th century lived in cities with step pyramid temples like the ones in Ancient Babylon, but had a near total literacy rate, which in most of the world was not seen until the 20th century. They made their weapons out of stone but they had gold metallurgy (the exception being the Tarascans that had bronze weapons) and used propulsors (atlatls) in warfare, that are more associated with Paleolithic hunters in Europe. They had no draft animals and so ignored the wheel, along with the potter's wheel and the windmill, but the Mayas built wheeled toys for children. And so on.
Meanwhile, the Incas in South America had pack animals (llamas) but no wheel nor carts, yet they built an extensive net of roads and forts to facilitate their conquests like the Romans did in the Old World. Their military organization also resembled Old World cultures (as noted by the Spanish that compared them to the Turks), displaying spearmen on Greek phalanx-like formation and using weapons, helmets and pectorals of bronze. The halberd, a weapon invented in Eurasia to fight armoured knights that did not exist in any shape in the Americas since horses went extinct there before they could be domesticated, was common. And yet, despite this well-built state structure the Incas never had writing: laws and history were memorized by people tasked with it, and math operations were done tying knots in kipus.
Some tribal societies in Africa rely mostly on their traditional ways, living in traditional huts and wearing traditional clothes, but can be seen carrying around AK-47s and other modern weaponry for defense in war-torn areas.
This trope is the reason given in thisReddit thread for why women find the "fedora persona" creepy and offputting rather than charming. It's not that it's not nice to be a gentleman; it's that it's jarringly unnatural to act like every Hollywood History interpretation of the 'gentleman' from between 1750 and 1950 at once.
Cuba and North Korea are sometimes described as Cold War anachronisms. Both are the sort of totalitarian communist states which largely disappeared from the world after the fall of the Berlin Wall.note China and Vietnam are still communist, but are now authoritarian rather than totalitarian. In addition, North Korea's military is still using the aging Soviet antiques they used to fight the Korean War in the 1950s. Cuba has anachronistic 1950s cars as a consequence of the equally anachronistic (but nevertheless continuing—although likely to end now that US-Cuban relations are being normalized) U.S. embargo.
Before Cuba and North Korea were Cold War anachronisms, Spain and Portugal were World War II anachronisms. In Franco's Spain and Salazar's Portugal, the old fascist Europe of Hitler and Mussolini quietly lasted into the 1970s.
A cityscape can come across as this trope, even a relatively new city such as an Australian city. The hodgepodge of architectural styles varies through over at least 150 years as you walk down the street; here are a row of the earliest houses in town, which are 19th century Queenslanders (there are multiple types); several commercial buildings built between 1884 and 1920, from neo-classical to mock Georgian; what was considered state-of-the-art in the 1930s... 50s... 60s... and on until you get to the latest buildings in town, whose structure may actually be wrapped around one of the earliest commercial buildings, directly across from a neo-Gothic cathedral with a horrid Art Deco facade stuck on the front and corrugated metal roofing, built in Victorian industrial red brick.
Some PBS programs have been known to use logos and/or slogans older than them. For example, Charlie Rose used the 2002 PBS logo until three years after it ended, Charlie Rose: The Week used the 2006 WNET logo until six years after it ended, and even today, POV is still using the former slogan for the National Endowment for the Arts, which sponsors the series and, at least according to the series, still believes that "a great nation deserves great art". An older example is American Masters continuing to use WNET's "Radar" logo for at least two more years after it was discontinued in favor of the then-current "WNET in Space" logo.
The Amish look this way, at least to outsiders. Due to their extremely conservative "plain" style of dress and highly selective approach to adopting modern technology (justified by their religious values) they can often appear at best old-fashioned but (despite common misconceptions) not in such a way that they stick to one particular era. This effect is heightened when they appear in their traditional dress in modern "English" surroundings, e.g. when you see them on the bus (which happens—many if not most Amish communities allow that). This circumstance is particularly common in certain parts of Pennsylvania, which has a large population of Amish and other "plain people" (e.g. Pennsylvania Dutch Mennonites), especially in their regional center around Lancaster; the weirdest (to the unfamiliar) is probably the large contingent of Amish/Pennsylvania Dutch merchants in Philadelphia's Reading Terminal Market, an enclosed (and rather bougie) market in the heart of Philadelphia's emphatically modern Center City (as in, "skyscrapers next door"), often using modern equipment to run their businesses. The laugh is on the unfamiliar: the Amish/Pennsylvania Dutch have been there since the beginning, drawn by the modern technology of the day (as the name implies, the market was the original Philadelphia terminal for the Reading Railroad, and the Amish were particularly interested in the giant refrigerated basement the market had when it was established in the mid-19th century).