It actually occurs to me that a NES could support up to six terrain types and have 39 countries (assuming each covered each terrain type), while still maintaining a glow-coast and auxiliary indicator colors of black, white, and gray (which eat up 22 colors or so; 19 for the sea, one for one of each). 38 if blank territory were left around in standard terrain colors.
Functionally, since most would have far less than all six, the total number would be somewhere around 70+, possibly.
It's difficult to get it to work for terrain though. I tried it with a LINESII map, and even after muting most of the terrain colors it's very difficult to get countries to stand out unless they use fairly bright colors (or if they're surrounded by mostly bright colors). It'd take some fine-tuning to work. It does work for elevations though, at least.