Hmmm... well, it took a few years, billions of $$$ and who knows ultimately the number of lives to figure out that the second Gulf of Tokin incident was a complete fabrication. They kept a lid on that for a while.
The sealed information on Kennedy's assasination has yet to be unsealed- think you'll be able to gleam any information from completely blacked-out documents? Or the ones they shredded or burned?