Hey nice discussion guys.
My take on it is this:
The big bad company did NOT know.
But SOMEONE working for WY did, and just like Burke was out for personal gain.
In my imagination, this would be someone fairly senior in WY who will either be someone in the prequel who knows about the Alien first hand, or got some kind of report - whether this is simply a translation of the signal or not doesn't matter.
This person then sneakily arranges for Ash to be put on the Nostromo as they know that is the ship which will go past the planet, they can't risk telling the higher ups about it as then administration steps in and there are no exclusive rights for anyone, nobody wins... so they give the order to Ash, they sit and wait.
Then sh*t happens and the ship blows up!!! Loosing all that ore, millions in adjusted dollars. The guy at the company craps his pants and covers it all up, no-one can trace it back to him, or knows what happens to the Nostromo.
He thanks his lucky stars there are no survivors, retries early on Earth with a nice pension, and dies 20 years later with the secret of the signal, derelict, Ash, Aliens, dieing with him.