Each contract was a certain number of machines and the start and finish 'C' Numbers for each contract can be found from various sources...The first and last engine/frame numbers are also still in various records...So, using these numbers it's then a case of working out how far into the contract a bike is and from that the matching 'C' number (for the tank) can be calculated...That's probably how Rik will have arrived at the number he suggested for your bike...
I have one of the lights that can be converted to the correct rear light for your bike..I'll donate it 'free gratis' to the project if you want it...It's not too difficult to do and is the only way to go really unless you get lucky (very) or you're prepared to spend a lot of cash if/when an original turns up....Ian
Yes the numbers are recorded but they're not always straight forward. If you look back at Rik's last post, he's already had a stab at calculating yours. Ron
Looking at numbers, C5110 commenced at WM20 5001 and the first machines arrived at RAOC Chilwell on 22nd September 1939. It looks as if the first 2000 were in accordance with the contract and were numbered C3928419 - C3931195. This would make yours, probably C3929645...unless perhaps Rob Miller can extrapolate anything different from the 'Key cards'.
Almost correct Rik! But according to the Key Cards, WM20.6227 comes from a block within contract C/5110 where the census number is 1 off the "logical" sequence. (And there were more census number anomalies in this contract by the way!) So WM20.6227 would have had census number C3929646 on the tank. And from the factory ledgers we know that it was despatched on 2/10/39.