Of course it doesn't prove anything. Everything we do is speculation. Still, probability is still a thing.
We
don't know the probabilities of people's fates outside the Nordics beyond "they obviously didn't come out unscathed". The Icelanders have two potential bases for
their immunity rates to offer for our pondering, genetics and old gods.
Both telegraph (pun intended) "things could easily be an order of magnitude different in the next country over". Most of the people presenting a case for survivors in their surroundings in this thread
assumed that immunity rates, rate of undeath+trollification, grosslings' tactics and problems etc. etc. would be the same as seen in the comic.
But, if you're feeling combative, let's flip the question: Which other places could maintain the levels of quarantine necessary to maintain a viable population, have the infrastructure necessary to support any form of investigation into the nature of the Rash and global radio communications, and (which was the original question) would make someone shell out for a world-encompassing radio?
For the records, I'm as much outspoken against "there would be survivors in place X
because I cannot imagine how the Rash could succeed in wiping them out" as I am opposing "everyone everywhere else is dead
because I cannot fathom how people could survive that". Unknown means
unknown, not "oh well, then the opposite must be true".
To address your question: I can name you one nation that I would
not expect to live up to the criteria you listed, and that's
ICELAND. Sure, they have the geographical isolation and had the coast guard to enforce the last bit of "nobody gets in, and we
mean nobody". But it's also an island that had quite limited resources ever since it got settled. The early settlers - less numerous than the Y90 population - relied heavily on fishing to keep themselves nourished; the presence of sea beasts (and scarcity of immune people to man the ships) threatens the feasibility of that approach now. Later, Iceland started trade/imports, from food to raw materials - heck, they're officially
still importing in Y90, from Bornholm produce to Pori timber to ore to ships (which Minna said to be a Norway-dominated industry) - which would have been outright impossible during the lockdown.
And
yet, the official answer to all these considerations is "plot says they managed, but not
how exactly. Deal with it."
And would anyone in The Silent World feel inclined to shell out for a short-wave radio on the off-chance that someone can get through to someone on the other side of the world who may or may not be alive/have something relevant to say? I'd say that money is spent on new flamers for a Cleanser squad.
I see amateur radio transceivers suitable for such communication and in
working condition getting sold for scrap value on flea markets (probably by the heirs of the original owner). World-spanning amateur radio frequencies get polluted by, e.g., fishermen in Indonesia who
somehow got their hands on even smaller transceivers. Marconi took five years to proceed from his first experiments to the world's first transatlantic transmission. For crying out loud, NASA astronauts leave more money behind in the parking lot at the Cape than one needs to get a cross-ocean radio link going.