nostromo

I don't believe it is noted in Alien. And it's 57 years after Alien ends that Ripley's found floating in space in the escape pod.

2122 AD

I believe it's meant to be 2122, 28 years after the Prometheus is destroyed.

Excellent. Then there are only 28 years between Pro' and Alien. I'd say no more than 5 movies left. :D

But red wolf. The ship on lv 426 crashed thousands of years before according to RS so Prometheus will never lead to Alien

As I recall, the Central Computer to Mother had a date 2137 on it, a whole 12 years later than the proposed date.

So 43 years between pro and alien... Nostromo investigates a distress call from an alien vessel. Who made the call? Perhaps David and Shaw, an engineer, maybe vickers?

As mentioned the remains in the derelict in Alien 1 were fossilized - suggesting that the remains were there for thousands of years, meaning that shaw and company will likely not interact with the derelict starship found in Alien and cause it to crash. So the distress call is just that - a distress call or warning from a member of the Engineer race looking for help from his people. Still, the prometheus arc could indirectly tie into Alien. Weyland-Yutani could still somehow uncover at least part of what happened to the Prometheus, and actually properly explore the mounds on LV-223. They might then extrapolate the destination(s) of one of the other ships, and track it to LV426. Not wanting to repeat the mistakes of the past (sending informed people who might reject the mission on learning of its potential outcomes like Shaw), they make a whole new set of mistakes allowing space tug-boat operators and an android secret-agent do the pickup.... just a thought. I would end the prometheus arc with a cutscene where Ash, Dallas, Lambert, Parker, Brett, and Kane are boarding the Nostromo while Ripley is ending a video call to her daughter, promising she'll be back for her 11th birthday.