Newbie Questions

I just downloaded Kawaks 1.49 the other day, and have been messing around with NEO GEO roms ever since, and I'm having a lot of fun. I was able to locate a BIOS, and renamed the files accordingly (000-lo.lo, etc.). Most of the roms I've downloaded have worked just fine, but a few crash Kawaks with a critical error or have major graphical corruption (I can tell right away on older games, the neo-geo logo screen comes up all scrambled). I would assume they are just bad roms, but they always seem to be the ones I really want to play (SS4, Metal Slug, etc.) Plus, I've gotten them all from the same source, so it wouldn't make sense for half of the roms to work and half of them to malfunction, would it?

Also, I see a lot of (set 2) and the like at the end of certain rom titles, and the files only contain one or two more additions, and are very small. What's the purpose of these?

Thanks in advance!