Sorry to be a pain! but I don't understand the dating formula. I have a BSA C15 without any paperwork/reg. The engine number is
C15 27702 and the frame is C15 6650.
Thanks for your help.
Bob M
You can date the bike on the BSAOC website;
http://www.bsaownersclub.co.uk/machine.html
You will see that the frame is from the 1961 season but the engine is earlier and comes from the 1959 season.
Thanks Julian