Originally Posted by
philosophiser
...I couldn't find any visible codes on the derailleurs, but the Shimano 333 hubs had "R N" and "R O" on the front and rear wheels, respectively.
Based on checking a lot of original bikes I have placed those "R x" codes as 1972 date codes. I'm less sure about the 2nd letter but I believe it equates to a 2-week period from the start of the year.