I remember being told that the the early script took you from a futuristic San Francisco, to Phobos and to various planets where WY was salvaging Derelict ships and tech. Also that Gibson's script was utilized at some point in the beginning, you fought both WY and UPP. You can see some traces of this in the Alien: Infestation game.
Every time they updated the story it was a major change. IIRC the Sephora with the new batch of Marines finding the Sulaco adrift in space was the only consistent element.