I think I may have figured out what the problem was. From time to time, with iTunes looking at a samba share for its library, a network hiccup will cause it to lose track of some music, and I think some of the genres I was seeing that were no longer used belong to tracks that had been dropped by iTunes but still existed where the library is actually located on disk. They just aren’t being picked up by iTunes because I had dropped the whole album from the iTunes library when I couldn’t find a bunch of the tracks. I’d just forgotten to add them back in. I think I should fix the iTunes library and then hopefully it and the Firefly library would match.