Hi Vincent, this has been covered before, but some time ago, so will explain for all "newcomers"
The Keycards are a piles of handwritten cards, and were made up, after the british Army went from the wartime Census, "C" number registration system to the postwar 2 letters, 2 digits, 2 letters system.
There were originally 2 sets of the same cards, one master set, that stayed in the UK, and a duplicate set that In the instance of the BSA/Matchless/Norton cards) went to Munchengladbach Germany, where the main office of the disposals department was housed, for the B.A.O.R. (British Army Over Rhine)
While all vehicle Keycards were donated by the Army to the Beverly Transport museum in the 70's, the bike ones were alreasy lost, or not deemed important and thrown away, or even stolen, we might never know.
After the Beverly museum went into receivership, the cards were duly given to the Royal Logistics museum in Deepcut, where all vehicle inquiries can be made, (exept the motorcycle ones, although they don't tell you that) for a fee of 50 or 60 pounds, regardles of what they find.
So back to the duplicates, the Colonel of the B.A.O.R. had the foresight to keep the Keycards of the bikes behind, when he was ordered in the 90's to clear out the disposals barracks in Munchengladbach, and everything else went into the bin!
So I inherited them from the Colonel, (he was a keen motorcyclist) who since has passed away, RIP Colin.
When this forum was started, and I got together with Henk and some other guys here in Holland, we recognized the information of the (BSA) cards, but a big drawback was that they were only searchable by the postwar British Registration number, that was often lost, when the bike was restored etc. etc.
So Henk invented a system, where every card was scanned both sides, and numbered, then all the info was manually transferred to an Excell spreadsheet, and the reg. number linked to a framenumber, so it was a searchable database.
Many thanks to Rob Miller, who I believe did the most of the work here!!
So exept 2 other people, Henk Joore and Rob Miller have the digital versions of the cards, while I also have the originals.
The information on the cards is free to ask for, but supply as much info as you have, framenumbers, C numbers, postwar military reg. numbers, (often supplied on rebuild plates) engine numbers are less important here.
I have been in contact with the RLC museum, but they are not very willing to join forces on the Key card systems, and we have the only searchable database, and with the help of volunteers, they could make their info a lot more accesible.
So basicly the data on my cards is free, only if you would like a scan of the entry of your bike, or a scan of the whole card (14 entries) than a fee is asked, this is nice to print out, and frame, a piece of history, although 99% postwar of the bike.
Sample of scan of 1 KeyCard, that has been posted before, if your bike is on it, you're lucky! original scans are high res. though.
Funds go toward the further digitalisation of the Matchless and Norton Keycards.
Here are the relevant BSA reg. numbers, if you have another combination, it's probably Matchless or Norton, or not bike at all!
BSA:
62 YC 40 To 99 YC 99
00 YD 01 To 99 YD 99
YE series not available
81 ZB 11 To 94 ZB 22
09 ZC 77 To 80 ZC 77 WITH SMALL GAPS
Now back to Vincents bike, 91941, is also in the cards, had postwar reg. no: 29YD31, C number 5125341
Sold on 16-02-1970 16th Base Vehicle Depot BAOR B41
Hope this clarifies everything??
Cheers,
Lex
email (option): welbike@welbike.net
What about Norton motorcycles? Do you have anything for my bikes? 
email (option): ferrarakias@hotmail.com
Kostas, the Key Card's are a record made when the British army attempted to sort out the confusion of wartime losses and post-war large scale disposals and to see just what they still had.
The best and most original machines which have not been contaminated by post-war use will not appear in the cards, neither will any disposed of prior to 1948 or so.
Your 1940 abandoned machine (with no evidence of any later service) couldn't possibly appear. Regrettably, the wartime records of what went where have definitely not survived and probably went in the bin during the early 1950s.