My framebuilding experience dates back to 1957, however, it wasn't until 1974 that I began a full time business and started recording frame numbers.
The frames built in England were stamped with a letter "M" followed by a digit that represented the year. M4 = 1974, M5 = 1975, M6 = 1976, and so on up to early 1979 when I moved to the United States. The digits that followed were a serial number that continued on from one year to the next.
I still have my original frame number record book from that period. Unfortunately it doesn't contain much info other than a number and the original customer's name. I does serve to identify one of my frames, as the year and serial number will have to match what is written in my book.

Dave Moulton

Below: The number after a name indicates more than one Dave Moulton built frame in the owner's colection.