Quoting Julian from an earlier response;
"Second, if the bike is registered at DVLA, a check on what history, if any, they have, using their downloadable form V888."
Just for any/all to note really, that the V888 process/requirements etc has changed dramatically recently and you CANNOT now just, simply, get the history of your vehicle solely because you own it!
We've had multiple rejections (they were all sent off at the same time) to such requests where previously for a fee (sometimes/sometimes none) DVLA would provide, if they have it, copious details of previous keepers, associated changes and changes to the machine details ie engine change.
With respect to this machine, I cannot understand why a Despatch Book search hasn't been requested by the OP. It would undoubtably confirm, or not, whether those numbers left the Factory together and when and to whom if they did.
Regards to all.
Paul.