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Sounds like Global Ignorance.
"A character is ignorant about basic geography knowledge; they are therefore stupid and should be shamed over it."
That sounds nothing like what I need or look for
Eskimos Aren't Real can be about countries, although in your example the characters don't know about those specific countries because they don't exist yet. So... Historical In-Joke ?
If I'm reading the example correctly, it's akin to time travelers from the year 3023 coming back to 2023 and saying "Hello year 2023 people, we are here to make a delivery from the country of Nerdo Crombezia" and we all pull out our smartphones and do a Google search and say "Huh? That's not a real country," even though it is (will be??) in the year 3023.
I had a glance through Time Travel Tropes, but it seems difficult because, like, of course nations rise, fall, and change their names over a grand time scope.
Edited by KD
It'd fall under It Will Never Catch On if they dismiss the country names as absurd and clearly made up
^^ It's more in tune "We've got those weird guns from those weird people, let's try to figure out from where they've came, because such quantity couldn't be made in a single shack or a workshop". That also accounting for being given few MRE rations that had "Made in USA" on them, which obviously was far less confusing than some unknown nations and countries. I've already checked Time Travel Tropes, hence the ticket - I found nothing that could be used for this, besides, it's not even time-travel specific (I think).
^ They don't. They are just puzzled about places they never heard, yet obviously must have giant industrial bases if they've managed to churn out thousands of AKs, being the big mystery what's even going on. Think in terms of 20,000 Leagues Under the Sea, where it's a big mystery about where the giant submarine could have been build in secrecy (on The Mysterious Island, of course), obviously requiring dockyards and funding.
Well, the example is time travel, but I can imagine the same thing going on with alternate dimensions, alien planets (requiring FTL travel), Hidden Elf Village... Then again - does everyone in the community which the characters come from not know about the place they don't believe exist? Because with time travel, alternate dimensions and so on, that would be the case. So it's not Global Ignorance (where the character doesn't know something easy to find out), or Eskimos Aren't Real (where the character doesn't know something a bit more obscure), but it's characters not knowing a thing they have no way to know. Historical In-Joke might work with time travel, but otherwise... I don't know.
Edited by Veanne
Is there any particular trope for situation where, for any given reason, characters declare a real, existing place to be non-existing or have no clue where it could possibly be, despite its obvious nature (to the audience)? Yes, I know there is Eskimos Aren't Real, but that feels like stretching it to the point of breaking.
The specific example that I have in mind is The Guns of the South, where the up-time travellers deliver guns from such places as "Yugoslavia" or "People's Republic of China". The readers know they are real and know what's up, but the down-time characters are puzzled where those places even are, after doing an extensive search through the books and maps they have access to, since none of the post-Cold War arsenals they are given access to won't be created for a next century.