> But the vaportrp.zip is the same as the vaportrx.zip.

Yep. The CHDs do differ though. It's handled as a fake clone since the roms are 100% identical. There are 2,3 other examples of that (natodef / natodefa is one). Fake clones have to exist, so the number of zips on the disk (split- or unmerged) match the number of supported sets.

Roman Scherzer
ClrMamePro