On both Subway Stamp Shop and Amos Advantage (Scott) websites, there are many supplements missing for the Minkus Global album. Unlike the Scott International album, Minkus worldwide supplements go in and out of print often. It's one reason I'd think people who collect the modern era (as opposed to the era up to the 1950s or so) might want to avoid that album. But that's just my opinion.
The Scott International XVI (16) supplement is identified as the 1980 supplement, not 1979. https://www.amosadvantage.com/produ...-US-Zimbabwe
Based on how Scott catalogue dates work, you might think the 1980 supplement to the International album would cover up to 1980, meaning stamps from 1979. But I've bought some of the earlier Scott International album supplements and they cover the years indicated for them, 1950-53, 1960-64, or whatever. And since neither Amos Advantage (the Scott website) nor Subway Stamp Shop goes out of their way to correct that, meaning that neither website says what years the supplements "really" cover, I'd imagine they in fact cover the years advertised for them. When in doubt, though, I'd just call them and ask. I'm betting XVI/16 (1980) covers stamps for 1980. They'd be getting a lot of returns if they didn't cover the year they're labeled for, wouldn't you think?