FWIW the serial numbers on my 1961 Super Rocket are a good example of what tampering looks like. The BSAOC identified several inconsistencies and declined to issue a dating certificate.
I believe this ‘56 Engine stamping (see pic below) is a correct example (and has been dated by the uk club) but who knows for certain eh. I have a couple of other spare CA10 cases with the same font. Some cases I have seen are relatively lightly stamped which can make the font tricky to recognise.
We should probably have a “sticky” thread on A10 engine and frame number validation.
PS I don’t worry about “revealing” numbers, its in plain sight on the bike!
PPS common “issues” with fonts on dodgy stampings are:
a “1” which is a plain vertical line (so it can be used as a letter and number so making the stamp set cheaper)
a “foot” on a number or letter where their should not be one (I am fairly sure a “1” should not have a “foot” but should have a “head”.
a “3” that is all curves but should have a straight section in the top half
A “7” that is all straight but should have a curved semi-vertical section
I’m sure there are other tell tale signs of dodgy stamps….on some years (maybe A10?) have slightly different heights for letters compared to numbers.
