I have developed a love for the lovely red saws and have wondered about this issue myself. So far as I can tell, the "champ" label didn't appear on all of the 670's, but I've not seen one without...except one very early model with no label at all! The "super" decal seemed to come and go, while I believe the 'west coast" thing was just a west coast thing, LOL. I bought some parts from an N. Cal dealer that suggested that the west coast saws had the K&N filter and hole in the top cover; this was a special-order thing by his distributor. My dealer in MN could order the same saw but did not have the "west coast" decal. They were not popular in Mn...no way to divert hot air from inside the cover to heat the carb on our mild winter days!
I think I saw a 670 on Ebay a while back that the seller called a "west coast", but had the regular top cover. I think, then, the truth is that all of them are just different labels for the same basic unit.