I'm hoping it's going to be about how the aliens got on board the derelict ship they found on Acheron (LV-426) where John Hurt got face-raped....that bloody big-arse thing growing out of the massive control-type seat they found would be an awesome story (I hope)....
[url]http://application.denofgeek.com/images/m/75spaceships/main/derelict.jpg[/url] Derelict ship.
[url]http://www.knowthemovies.com/wp-content/uploads/2009/06/alien-1979-screen-1.jpg[/url] The "Pilot".

Unless another elephantine entity decided to go for an ill-fated joyride with those buggers aboard, I don't see how they would have existed in the regions of space mankind had explored at the time.