Even if the X-plane project was part of the conspiracy, the sheer numbers of people involved would make it nearly impossible to keep under wraps. When you include your icewall guards, pilots and aircrew, manufactures of windows that make things look curved, the scientists and astronomers, ground crew for the fake satellite vehicles, photoshoppers for NASA, and the admin staff for ALL of the said people, thats a major part of the population involved. There is absolutely no way that kind of a secret would be kept under wraps.
The term 'need to know' isn't just a movie slogan- its a golden rule of keeping operational security. People talk. Whether its to their wives, to their buddies when they've had a few, or to an agent of an FIS. The way to stop this is, obviously, to keep the number of people involved to an absolute minimum.
Unless, of course, the conspiracy doesn't exist. Then you wouldn't have to worry about evidence of a non-existent conspiracy getting out.