If you do not have a full MAME romset then you shouldnt of used the MAME fullset importer. That importer does not scan your files at all, it assumes you have a fullset and imports all working roms via a metadata file. If you have a handpicked set you should use the standard rom importer, otherwise you are going to have tons of games that dont work as you dont actually have the rom files for them, but they will show in Launchbox.