My gut is telling me that the issue is not GameEx as in a bug but a limitation. The database files are by system, not by emulator. Since MESS is derivative from MAME, some of the conventions for naming should remain the same or similar. This is the case when reviewing the MESS a7800.xml file. I noticed that my ROMS and snaps do not follow that same convention (in MESS) and are more closely aligned with the 7800.mdb naming convention (in GameEx and likely Hyperlist - which is how EmuMovies provides a lot of the snaps). If one could create, as Tempest suggested, an mdb file from the MESS xxxx.xml files and GameEx could be modified to allow for selection of the .mdb dependent upon the emulator in use, that may work. In the interim, the .mdb file created as per Tempest's suggestion could replace the one provided by GameEx by default. One will have to consider that the other emulators for the other systems may not necessarily follow MESS's naming conventions.