Frame & duplicated frame number 10922 are in my Register. This bike was offered for sale by Andy Tiernan in 2019, and it reappeared in July of this year when it was sold on eBay. I guess that's where you bought it.
But... the engine was (and probably still is) a side valve, not an overhead valve. And the bike has a center stand, not a rear stand. Which makes it a WD/C, not a WD/CO. It was despatched to the War Department on 23rd April 1941, under contract C/7182. This was an RASC contract for 6000 bikes (frame numbers 5901 - 11900). Census numbers for pre-RAOC-RASC-amalgamation RASC contracts can unfortunately not be calculated. On top of that, there were 4, maybe 6 blocks of census numbers. It is all very confusing. Considering that this bike is approximately the 1000th bike of this contract counting backwards, the census number must have been somewhere in the late C989XXX - early C990XXX region. See also table below.
I've also added a picture of a bike that could have been yours (census number C989981, source: IWM H28662). The picture was taken at an officers' training school in March 1943. %%htmlItem_3%%
