Easton Swift shafts were made in the 60s and were fairly soft and bent pretty easily-but if you didn't hit anything hard-they were just fine. I still have at least 15-20 dozen Swifts in various sizes. The 24SRT-X was the first XX75 alloy, far superior in strength, and-to my knowledge they were all silver in color and only differentiated from the Swifts by the imprinted logo. Those two products did overlap for a while. Easton really differentiated the XX75 with the introduction of Autumn Orange anodized shafts. Shortly thereafter the Game Getter came out. It was softer than the XX75s, bent more easily, and it's color rubbed off, as it was not anodized. As with the Swifts, whatever the alloy, one Easton aluminum shaft was as consistent as another. The XXs simply had better strength and bending resistance. For me, the Autumn Orange was the epitome of aluminum shafts, and is a bit of a tradition of it's own! More recently, Game Getters come in the XX75 material(anodized & camo'd) and there are other alloys as well. I believe X7 was later than the others and now the top of the line....also have seen reference to an XX78? I can't claim to be up on all of those.
These may not be all the facts-just the impressions I can remember.