If you wan to audit your games, get a rom auditing tool such as RomCenter and the proper Neo-Geo DAT for it. As for Nebula Loader ( and Loaders in general), you don't need to worry about CRCs. You can put whatever CRCs and filenames into the DAT and Nebula Loader will try to load the files (NeoRAGEx works in a very similar fashion). Of course, the original FBA, Kawaks, Nebula and MAME only load certain sets because of hardcoded values. Nebula and Kawaks Loader can also work with encrypted sets to a degree, but you'd have to know the right GxfKey value for that. True there are a whole lot of sets. KLR Freelance is a pretty good site because it lists the files CRCs and sizes for most of the newer sets. Decrypted sets take less space, but all of the post 1999 *original* sets are encrypted because that's how they were on the real arcade PCB. Sure, after a while, decrypted sets surfaced, because people who like more simpler emulators (like NRX) wanted to play those games too.