Looks like I've realized there's a few I've already forgotten:

6. Protoforms. I guess they could either be their own category or even lumped in with cast or quasi-cast.

7. Movie repaints of movie repaints. This includes Recon Barricade, Jungle Boncrusher, Salvage and Overcast.

8. Exclusives. The red Starscream, the Aveo, the pink Arcee, etc. Was Black Arcee an exclusive or was that her standard Takara coloring, like Incinerator?

I'm still lost as to the three I mentioned. Perhaps they would all just go in group 7.?