Some things, for some reason, aren't as easy for me to remember as others, i know KP or Chris remember better than I.
Early covers had no date stampings.
Stampings seen on later covers as well as other parts such as inside of cam covers have date stampings based on the Showan Calendar system. Hiro Hito (family Showa) began his reign in 1925; 1969 was the 44th year of the emperor's reign. So, if i remember accurately, the date stampings start with the year "44" then followed by month then by day; e.g., 44.9.26 - 44th year of emperor's reign, 9th month, 26th day or as we say it, September 26, 1969.
I think KP has archived in his personal pictures ink date stampings on CB750 parts. Someday, i believe, he plans to get them posted on the website or the BB.