It's obvious from Special Order 937 that Weyland-Yutani had somehow already detected the warning beacon emanating from the derelict on LV-426, and had at least partially deciphered it. Is it ever explained anywhere how and when they managed to pick up the signal and decipher it? I've always assumed that the events of Alien were the first time humans had ever encountered the xenomorphs and that Weyland-Yutani knew very little about them other than that they were dangerous. I've also wondered if the company always knew immediately that it wasn't a distress signal, as any ship passing by before the Nostromo would have been required to investigate it, is that right?
According to the viral website ProjectPrometheus.com (transcribed below from yutani.studio), Weyland Yutani discovered a faint signal emanating from LV-426 as part of their deep space exploration, likely in 2078 or 2079. It was one of the reasons that Peter Wayland authorised a trip to LV-223, a nearby planet in the same system. They presumably (partially) deciphered it at much the same time.
As fate would have it, Shaw and Holloway’s interest in Zeta 2 Reticuli has proven to be mutually beneficial. While the good doctors rely on ancient carvings and primitive cave paintings, my science division’s own long range scans have recently detected a faint, almost imperceptible signal emanating from one of the lesser moons in that system. And contrary to the findings of Shaw and Holloway, which target LV-223 as our primary site of interest, our findings suggest the point of origin could actually be the moon LV-426.
Per standard procedure, we will embed a David 8 unit with the crew. and he will be programmed with multiple contingency plans to address and exploit whatever assets we secure on 223. But only David will know about 426 and will ensure that the rest of the crew- including Meredith – learn nothing about the transmission we’ve recently discovered until the time is right.
For if Yutani’s new ECIU software is to be trusted, there might be great risk awaiting us on the path to an even greater reward.