Easy way to check if a game is from PS+ is to check it's expiration date. If you own it, it won't have one. PS+ games expire when your sub expires. When I let my PS+ expire, I bought the games I wanted continued access to, unfortunatley like 10 or so were delisted so I'm SOL there. Sounds like the store is even more of a mess now though, glad I don't (think I) need anything else.
Nearly all downloaded games (both purchased and PS+) had an area under "Information" for the activation and expiration. If you bought the game, expiration was set to never or something similar. Oddity of the bunch was TMNT: Out of the Shadows. It didn't have that section at all. After a quick Google search, it seems the title was only $15 at launch, was never provided for free and never provided as a PS+ monthly game. So, I should be in the clear with "Owning" it.
