Hmmmmm......
I think the current assignment of "common" and "all" is already ok. Merging between different systems hmmmm....iirc I made it an "all" statement since it's not such important anymore either.....if you keep the sets separated, they are handled correctly. If fully merged, they belong to the parent's system which is ok, too.

I doubt I will change it. For MAME, keep it on Show Common. Everything else is not recommended.

Roman Scherzer
ClrMamePro