I emailed Honda Uk at
info.uk@honda-eu.com for a dating certificate, to get my 1985-registered CB750F correctly listed as manufactured 1983, to enable Historic status.
They will email back to confirm if they have the info you require, at which point there is a fee for the dating cert. I then sent the cert to DVLA along with a covering letter, the old V5c and a self-addressed stamped envelope with a request that they return the dating cert afterwards.
DVLA returned everything, saying their records had been updated and that I now had to take the new V5c to a vehicle licencing Post Office to declare it as Historic taxation class - but there was nothing on the replacement V5c to say the date of manufacture!
I went to the Post Office (armed with dating cert, MOT exemption declaration and V5c) expecting an argument, the lass scanned the barcode and obviously something on the DVLA system had been altered even though there was nothing about date of manufacture on the V5c, as she just accepted it and processed the application. 2 weeks later I got the new V5c through the post with the bike now listed as "Historic" taxation class.