A good few years ago I bought a Q plate xs1100. It had matching numbers and was imported from Holland. I contacted Yamaha UK with frame and engine numbers. They sent me a letter stating it was a 1979 model imported to Europe. I forwarded this onto DVLA and was issued with an age related plate.
A couple of years back I also bought a Triumph Speed Twin also on a Q plate. This bike also had matching numbers, so this time I contacted the Triumph Owners Club, supplied them with pics of the engine and frame numbers, and they then gave me a dating certificate that it was a 1959 model. This time I had to get a VOSA inspection which was straightforward and I was, again, issued with an age related plate.
Neither was an overly complicated piece of business and both hinged on the dating letter from the appropriate 'specialist' so as stated above contact Mr Dawkins, whose name has been used a number of times on this forum