Like so many things, there isn't actually a true answer to this. I have an 89 FJ62, have had it for 18 years. That doesn't make me the authority, but this is what I've seen. The FJ80 was introduced in late 89 in Japan and was sold as a 1990 model in the states. The 60 series was produced through 1990 in Japan, and through 92 in South America. I think you won't find many 1990 62's, although they do exist. You also won't find many 1990 80 series because they didn't ramp up production fast enough, and they really didn't become popular right away.
Wikipedia says the 60 series was 80-89 and the 80 was 90-97. Also Spectre Off Road who has a long standing relationship with Araco(Land Cruiser body builder) in Japan, shows the 60 series ending in 89 and the 80 series starting in 90.
https://www.sor.com/catmodel.sor?backto=CATINDEX.sor
Just sayin'