I picked up an NEW M91 at the Austin Gun Show this weekend. (Still here that round going off)...but it is so lightly stamped you can't read the date. Is there any other way to confirm its age? You can barely make it out that it even says New England Westinghouse. It is the straight stamp. None of the serial numbers match.. in fact the butt plate has two serial numbers, one with a small hammer over it.