Upvote:2
Its possible I can narrow it down further, due to there being no red box in the Pacific for the Trust Territory of the Pacific Islands. That puts it at 1986 or later.
Upvote:3
I've found this wikipedia page, which is precisely the list of "things I have to check" for this investigation.
It allowed me to raise the lower bound to be definitely 1984, and I doubt we can then get more precise than 1984-1990. Still, maybe I missed something, so better answers are welcome.