I've never personally seen a single-digit S&W serial either, but I've read different authorities on the subject state that, prior to 1982, S&W would always omit the preceding zeroes after an alphabetical prefix. For example, C-series postwar K frames started at C1 rather than C000001, and proceeded through C9, C99, C999, C9999, etc. This system continued when S&W used the "wandering J" and "wandering K" in the 70s, e.g. the 5K prefix started with s/n 5K1.I've never seen a serial number like those on Smith and Wesson revolvers.