Factory Letter info. is taken from the shipping ledgers which record the day the gun left the factroy to a distributor or dealer. The BATF uses this date to determine the gun's classification or age for their purposes, except when the factory separately identifies certain guns made before 1898 but shipped many years later ( The date the frame was made controls) For example, all Model 3 .44DAs are antiques, although many were not assembled and shipped until years after their pre-1898 frame production dates. There are records in the CVHM archives and other places that give the manufacturing dates and/or the dates the finished gun was sent to the vault and available for shipping when an order was received, but these records are scattered and not easily accessable, or are in private hands, such as the Floor Foreman's Day Books, circa 1880s-1890s, etc., which show guns by serial numbers and dates as they go thru the asssembly & finishing steps. Hope that helps! Ed #15