I played today on sidearms on 2 versions mame: 36b15 and 81. On version 36b15 default difficulty is set to 0 (easiest), on v81 is set to 3 (normal). Which settings is correct?
I would presume that someone actually found what the factory settings are and changed that in MAME accordingly. Some CPS-1 games (and a few others too) have some absolutely ridiculous defaults.