So both of my model 1 systems appear to be non-TMSS, but the second one won't load Populous. No Sega message for any cart though.
Nice! You seem to have the complete opposite luck as me.
I'll have to keep digging, I might have more Genesis systems laying around somewhere. I know I have a bunch of model 2 systems in a box with some other junk, but I'm not sure about model 1 systems.
I sat there for about a half hour trying to get Populous to load on the other model 1. I popped in Ranger X, Sonic and Knuckles, and X-men. They all worked no issue first try with no Sega message. Populous just wouldn't load. It kind of defeats the purpose of a non-TMSS model if it won't load the game. *shrug*