Yeah, there is always this to fall back on, but... I hope to present a world which is a bit more ambitious in its coherency. Admittedly with very mixed results, since the subject of secret alien invasion is really hard to pull off...
A balance has to be struck somewhere, because if not we'd be bogged down in trivial issues like "given that X-COM has hundreds of agents as well as non-combat staff by the time the invasion starts heating up, how is it that not even one of them has said too much about their work to the wrong person and consequently obliterated anything resembling secrecy several times over?"
(Incidentally, this is also why most real world conspiracies tend to stay very small and have less ambitious goals than anything you'd see in The X-Files- people in general are terrible at keeping secrets.)