Survivors of Benghazi were also sworn to secrecy and, no doubt, subject to threats.
Yet, some have talked.
And Benghazi was only four years ago; TW800 was 24 years ago.
Besides which, I question whether the USN would ever conduct a missile exercise in waters like Long Island Sound. It's shallow, it's narrow...and the air space is crowded with commercial traffic.
I'm not getting your point here, and I don't see what Benghazi has to do with this. At the very least, you are extremely uncreative. People stay silent for many reasons, not just threats. Is it beyond your ability to imagine they were told they were preventing a catastrophe? That they were told a nuke was on the plane, or a biological terrorism threat of some kind, and they had just minutes to act? Cover stories create a DESIRE to remain silent, to regret the loss of life but see it in a bigger context.
Benghazi, on the other hand, was understood by operatives as to its real purpose. So they can only be threatened, not lied to or misdirected.
The game is far deeper than you realize.