Tom The reason they have all surfaced at once is the internet. A very few years ago a handfull of collectors were the only ones with contact with each other. Like most of us owners of these guns, who are not collectors, I had no idea mine was marked any different than all the rest till I started checking on what it might be worth. I figured it being Full Choke was different, but that was about it. I have seen a couple US marked shotguns over the years, I think all were 97's. I had no idea how a WWII Military Model 12 was normally marked before I started my search. I still have no idea how a WWI Model 12 was marked.
If both of the last 2 guns listed are marked the same as the first 3 we now have 5 early M12's found with around a 2800 spread in the serial numbers 92635X to 9291XX.
And the search continues for more.