Hya pasty...
I believe it goes on the frame no. + a little help from the VJMC if it's to do with convincing Swansea DVLA.
You didn't mention what bike it was.?
For the Cb750 for example, there is a little lee way , as in the early days of manufacture , most went to the USA and we had to wait...
A bike that was registered in this country say in Aprill for example, may well have been built the year before.
What is your bike, and what is the frame number?
I have a few books I can look in, but if its borderline you will need the VJMC.
Kaceyk2