These mk2s are as rare as the US Navy.
We can't talk about limited series or prototypes, but rather a few test copies. I only listed a few parts.
Yes, mine like Blancpain's (exhibited in 2013 in Basel for the FF's anniversary) and Phillip's do not have a case back number.
I don't think old watch case have been modified, but the use of new ones with a case back similar to the first TR900/ series. Chronologically, they are in my opinion the latest evolution of the military Milspec with a derivative of the calibre 1361
Unfortunately, US NAVY didn't choose them... And their story is over, probably Blancpain's too.
We can talk about dead projects born like Air Command.