I wonder if there really is a secret code or if it was just mentioned in the Boss Book to add to the mystique (if such a thing exists) around Boss pedals. ha ha ha! But seriously, I think I personally am much better off NOT knowing how to date them by serial number or batch number! Imagine how bad it would be... "Well, I have a 1981 OD1, a 1982 OD1, now I need a 1980 OD1"!!!