Besides the many Exage groups, there's also some overlap with some models. My Exage 500 CX rear derailleur is nearly identical to my Deore LX long cage RD. Even the model numbers differ only by a minor increment. And there are small cosmetic differences. Both are 7-speed for index systems, but with Deore 8-speed bar-end shifters set to friction mode both rear derailleurs will cover the 8-speed cassette I used to replace the original 7-speed on my early 1990s Univega.