I do understand the rule, but less the fact that some baseplates would have been changed on S-IIs. Why? Unless there is a psychological explanation: MIOJ (= made in occupied Japan) would have been infamous for some owners? Like the inscription " Luftwaffen Eigentum" sometimes erased on wartime Leicas?
BTW, my "Canon Seiki Kogaku" S-II had the s/n 15492, with the Serenar 8322 (Seiki Kogaku too). So, probably a preseries one, by Jim. When I think I sold it....