The Winchester model 21 shotgun has been made since 1930-1931.These shotguns were still being made by there custom shop in 2007.While I have the serial numbers by year for 1930-1941,after that Winchester did not release these figures.The last serial number in 1941 was 10475.You may find the year of manufacture by contacting the Cody Firearms Museum located in Cody,Wyoming.They will for a fee authenticate your Winchester model 21 and send you a fine letter describing the year of build,special order features found on your shotgun,date shipped and to who.This fine letter from Winchester will add value to your shotgun,and can answer all your questions about it.