TCRF mentions Teenage Mutant Ninja Turtles (Arcade) - The Cutting Room Floor that the JP version of TMNT (the actual arcade version) fixes a scoring exploit from the other versions where you could destroy infinitely recurring projectiles for points. (Oh hey I guess that applied to the US NES version too, as daphaknee mentions it as well. : ) They don’t mention any actual difficulty-related differences.
HM but yeah it is a later revision so I probably should be playing that one anyway. : D Thanks for mentioning it!