Not sure I agree that the hobby would fall on its face if GM had (has) them, and then released them. I think about PHS and the Marti reports, which seem to verify things for the Pontiacs and Ford/Mercury guys. Would there be some lawsuits? sure, but I think it would be on a small percentage of cars. When the NCRS all of a sudden had access to find out which dealer your car came from and the date it was produced, that may have led some guys to realize their cars docs and some components were fake, and may have resulted in some law suits, but I think many guys that don't bother to research, and just take the seller at their word, probably also didn't take the time to order that from the NCRS. I also believe there is a small percentage of us that can recognize a real window sticker vs. a fake.
William, Kurt, James, and others on here, have been great on weighing in on authenticity, and I believe has helped many of us learn how to spot originals, vs. helping the fraudsters make better fakes. There is no way of knowing this, but I am going off of how many fakes are still spotted, or mismatched cars that all of a sudden pop up with an original drivetrain. Hell I thought I found a window sticker from the same dealer as my car, (it was with a 68 Corvair), and it was a fake. So yes fakes are al over, but as Jimmy V alluded to, you have to check over all the docs and stamps.
I agree with Tim though the water mark, or identify-er should be on the front of the window sticker, make that much harder to duplicate, or that much easier to identify as a reproduction.