I used to own a B10 four door sedan that was originally registered new in February 1970. The chassis number was B10-305152. I'd guess you'd have to allow four months from being manufactured in Japan to being registred here in the UK at least so that would make it late 1969.
I have a Swiss Datsun brochure that, although not dated mentions production figures as-of November 1969. That brochure still shows the B10 in the model line up, although strangely the model shown appears to be a '68.