The date i used was based on Scott saying the story took place 30 years before Alien and i read it was supposed to be in 2092 or maybe i got it wrong it's Ripley's birth date.
As for the fosilised Space Jockey, maybe the answer is Time Travel.
When space Jockeys travel they may bend time and space, and sometimes maybe it goes wrong leaving this one stranded on LV426 way before humans reached the stars.
Or that ship was lauched by the Space Jockey eons ego and the space Jockey Race is still alive at the time the nostromo discover the derelict but in another galaxy.
Either way we are not going to see LV426's Derelict in PROMETHEUS.
Neither the xenomorph we know.
There's no eggs.
Ridley kept saying he wanted something fresh, saying that the facehugger, eggs and all are not scary anymore.
BS guys.