The term "NOS" means "New
Old Stock" and there's nothing old about these parts. These are brand new, recently manufacture service parts from Omega. The "NOS" crap all started with Watchco claiming they had all these "old" service cases, when all they were doing is buying brand new, recently manufactured, parts from Omega. These are not old, therefore are not NOS watches or parts.
With that out of the way, let's look at the case designs...here is a case that was manufactured in 2016 from what I recall on the package:
Note the shape of the cut out at the crown guards:
The "A" in waterproof is flat on top:
These are images I've just taken of a case I purchased right from Omega recently. This case was made in the 25th week of 2019, so just a few months ago. You can see the date code on the package:
Front shot:
Note the cut out is very different for the crown guards:
And the case back has a pointed "A" in waterproof:
Again, both of these cases were purchased directly from Omega, so there is no doubt regarding their authenticity. I do admit that last year when the photos of the different cut out for the crown guard were first posted, I was skeptical that it was an original Omega case, as there are fakes out there. But having ordered one right from Omega, I am satisfied this is now a change that the cases have gone through.
Cheers, Al