Thanks folks for your responses! The term "key" is used in a lot of the documents, so I wasn't sure which one applied in this particular case. Thanks also for pointing out the exact version; this is helpful. I see that this may affect other Capcom ROMs.

After running mame64 0176 for a while, I recently updated to 0180 and noticed a few ROMs that used to work were now missing files. When using "mame64 -listroms <rom>" a new entry was present relative to 0176. Namely <rom>.key, where <rom> is the name of that particular <rom>.zip file. This...