Yes, never underestimate a greedy corporate executive when it comes down to securing the exclusive rights to some bioweapons tech. Weyland Yutani might have the entire truth of the Xenomorphs but because everyone wants their cut of the profits the information is massively compartmentalised. Its a fun trope for big evil scifi corporations in that many cases the left hand doesn't know what the right hand is doing.
I agree. But what is really ”the entire truth of the Xenomorphs”? Is it just what we see in the movies or is it something more? Perhaps a lot more? We as fans only have a vague idea of who the Engineers really are, where they came from and what their connection to the xenomorphs really is (yes, I know all that stuff about David, but you can ignore that if you like). I imagine a large, interstellar Lovecraftian mythos of more or less bizarre beings somewhere out there. I don’t think they should ever be fully described (it would kill the mystery), but perhaps hinted through strange artefacts and ruins. Again: it’a up to each individual GM.
So to answer the initial question in this thread in a slightly new way (instead of just commenting the most recent posts, although they are interesting): it seems reasonable that there is a much bigger picture than seen in the movies. It might involve many other expeditions and bizarre encounters. The Company might even have established some kind of contact with the Engineers - or at at least recieved more signals from other locations. You can include whatever you like, even a lot of stuff outside the official canon. Or you can stick to the movies in a very orthodox manner. I personally view canon as something to play around with. Others probably have a more strict approach, which is also fine. But making some kind of decision is probably a good answer to the initial question.