Just to play devil's advocate... How many people knew about Enigma/Ultra after WWII, and yet the story doesn't appear in any WWII history I've read until the 1980's, at which point it became headline news and the subject of innumerable "The History Channel" documentaries. Not only did the victorious Allies keep the secret, but no one on the defeated Axis side spilled the beans publicly, even though it might have mollified their pride.

On the other hand, I've heard it said that the Manhattan Project was relatively "leaky," and that it succeeded, not because it was tippy-top secret, but simply because there was nothing any enemy could possibly do to interfere with it.

I can work out a couple of
"Lunar Hoax" scenarios that keep the inside committee down to a few hundred people...but that's reverse-engineering: it presumes a successful hoax and tries to construct a scenario to support it. Real conspiracies don't work that way.

Silas