I'm not an expert on the rotor versions by any means, but besides the color kits and graphic differences year to year, there were a couple of things I noticed on older rotors.
The first is the addition of the "shark tail" on the newer models. The anti jam red piece in the feed tray was modified to have a second longer piece in addition to the smaller curved front piece. You can buy the updated rip drive piece as a standalone part.
The second is the change of screw heads on the top shell. They used to be allen screws and they switched to Phillip's head screws. Useful for when you want to install speed feeds.
Probably are other things, but those were the two I noticed.