My guess is it's legit. The early ones weren't U.S. marked and it's in the correct serial range as built in 1919. I have one just like it, sn. E683164 built in 1918 and the "US" was hand stamped on just in front of the ejection port after rebuild at ordnance workshops at some point. I imported it along with several others when we could get retransfer authorization from U.S. Department of State. The majority came via Canadaicon from Vietnam.