It's been what I think explains the appearence differences between the LV426 Aliens and the Antarctica Aliens in AvP.
That's actually just because AVP is garbage and uses garbage.
And from what we've seen so far in the original films I don't think so.
The Alien in Alien and Aliens in Aliens all came from the same place, there's loads of theories floating about such as the they are two different types or as Cameron stated that his were older. Alien3 we know it's because it came from an animal, in most people's preference an ox. So that difference is explained. (Leg design changes and slight other changes are purely aesthetic if you take A:I into account, and there are slight variations in Aliens also.)
The Resurrection Aliens are just a biological mess, I would hesitate to even call them Aliens.
The vials in the vases in Prometheus produce Alien-like creatures but I would refer to them as cousins at most. (Alligator to Crocodile)
The Leg design and the other changes were meant to be because of a different host, but Resurrection screwed that up along with silly design changes, fleshy look and so on. I wonder if there was explanation for it behind the scenes, its been awhile since I watched them.
As for Prometheus creatures, I agree, they are not proto-Xenomorphs no matter how someone wishes it, there is a connection kind like crocodile - Alligator, I would have said Caimen
but nothing else, I would say the accelerent is much more deadly than Xenomorphs because its more infections and random, not even Xenos are immune to it.