The 1955 date would seem incongruous with the stamping of "S.U. (sic) Service Ctg." The .38 Colt cartridge was the U.S. service from 1892 until 1911, and was issued through 1918 or so.
Since the .38 Special dated from 1905, I'm guseeing the age between 1905~1920. And that is the period of Belgian copies.