It's not off topic Lee. Henk change the forum from WD M20 to WD Motorcycle a couple of years ago.
The last CO frame number in O&M is 30037. But there were a few more after that which aren't listed. Probably Jan knows. Ron
In addition to the information that Mick just gave. It's 1942. CO/B means it was built with a Burman gearbox. Presumably During a period of shortage of Albion box's. I have an original CO/B workshop maintenance manual for sale if you need it.
#16913 is a contract C/13870 (WD/CO/B, with Burman gearbox) motorcycle that was despatched on August 23rd 1943. I'll send you a link to my Report on the WD/CO, in which you'll find all the info you need!