Interesting indeed. Is it correct that only the K's were being stamped for Gretsch?
The K's that were sold out of the Gretsch warehouse were. But not just the K's either. Ajahas sold from there were similarly stamped with the "G".
This pair is an exceptionally rare find. It looks to me like from the front-side shot that the paper label on the right cymbal was originally pasted on top. I concluded this by the greenish rectangular area which is apparent in that view. Weird things like that did happen from time to time. I still have a 22" old stamp that came with the paper label pasted right on top of the signature.