On low grade Smith guns one will often find miss-stamps, overstamps, and the occassional double stamp as regards serial numbers, patent dates, and barrel markings. All were cosmetic errors/mistakes of some type; but only guns with glaring problems were rejected by the inspector, although some blemishes may have caused the gun to be discounted to the original purchaser. As to the rarity of a "Hunter Arms Fulton NY" double stamp, who knows? No records were ever kept of such anomalties. Do such mistakes increase the value of a gun like a double date stamp on a coin? Not to my knowlege; and I personally know no collector who collects factory blemished guns. Collectors generally want specimens that are as near perfect as possible, and are likely to discount any gun with visible surface blemishes; factory or aftermarket.