Or. Maybe the engineer on LV-426 is David, and the thing that bursts out of him is the Queen chestburster? after he uses Daniels reproductive organs to make the queen. It escapes and dies somehow to events not portrayed in any movie yet. And all of the eggs in the derelict are the crew of the covenant turned into eggs via egg morphing via his experiments?
Or he made a queen to make all of the eggs inside the derelict instead and we dont use the egg morphing method. And now we're left not only with the reasoning behind biomechanic aliens because he used himself as a host. But we also have the Queen > eggs life cycle set up.
When the crew of the Nostromo find the space jockey, it's not at all fossilized, it just appears to be because of the way the suit is made from bone/alien biomechanical space jockey tech. (Which i can forgive because the Jockey suit was already different visually in Prometheus)