The cover could have been used on any post 1948 heavyweight civilian BSA single...B31/33, M20/21/33, ZB32/34 etc...(not late Gold Stars though)...The 'winged B', later font style and revised breather location were introduced for '48...Ian
The breather was located in the timing cover on the models detailed from 1948...
Earlier models such as the later WB30s also employed the breather in that position but not with the winged logo...Earlier B31s had the breather behind the main bearing in the drive side crankcase..Later pre 48 models had it in the crank case as on the M Series models...None before 1948 used the winged logo and later font style..
In this case it's the particular combination of the various features that make this cover post '48...Ian
OTOH it fits
so if that's the only one you have then ride with it on
Sooner or latter some one will tell you it is wrong ( that will make them feel happy ) and with a bit of luck they or some one else will have a correct one.
Over the years I have scored dozens of parts that way, all you have to do is be polite and waste a few hours talking to people who walk over to have a chat . About 1 in 10 will have some thing worth while to say.
We were sitting ata McDonalds one day & a bloke came over to have a chat
HE had 20 old bikes a tennant left behind on his trailer about to go to the tip .
Of course they never made it there and the entire lot had several very rare cycle motors worth thousands .
I dont go to auto jumbles that often, so what is something like this worth nowadays ? Its superfluous to my needs so does not need to sit on my shelf!
Richard.