There is no information on 28 gauge originality at Cody. There is no serial number that "books" as a 28 gauge. Anyone can punch a 28 on the back of a receiver. As Sam H. says, the cutoff slot can be both ways. I have been buying Model 12s for fifty years, have a very nice collection, but I would not touch a 28 gauge at retail prices or half of retail. They are too hard to buy and too hard to sell.