Seems to make some sense that maybe when the shiz goes down on LV 223, some 2000 years ago "give or take", one of the infected engineers fled site in one of the many other ships and crashed onto LV 426 when he died? This would be more likely if they are orbiting the same planet and give enough time (1.6-2 millennia) for the derelict and its contents to ossify by the time it is found in 2122 by the Nostromo.
As to the star maps pointing humanity to LV223...
I tend to think that the engineers encountered the xenos (or precursors/variants of them) hundreds of thousands of years ago. Through their own tribulations with the species and subsequent study of them, they discovered its ability to alter/recombine DNA and eventually leveraged this to seed life across a multitude of worlds over the millennia. This would almost explain their reverence of the biological cycle of egg-facehugger-anymorph as almost a religion then depicted in the murals and sculpture.
Furthermore, that would explain the Deacon and its existence (or something very much similar) in the relief sculpture. Maybe the Deacon is the result of a Xenospecies + Engineer pairing (although the one we saw was achieved in a roundabout manner) and allowed them to study and extract the raw "accelerant" black goo for their purposes. After they've got the stuff, they start bouncing around the galaxy seeding various planets through the sacrificial fusion of the goo and their own DNA.
On the flip side, if the goo has already been infused with additional material, that could lead to the weaponization of the stuff. In early scripts, this goo was represented as scarabs, and it was eluded to that there were variations of these scarabs, based on each groups source DNA in other areas of the ship. Could be that each variant was based on the union of the xenospecies with each dominant lifeform from the planets they had seeded.
In any case... It may have been that, when the engineers identified LV 223 to early man, it was before the moon contained weaponized forms of the biomass, only the raw, untainted accelerant they used to seed life.
Just speculation of course.
