I'm pretty sure the Vintage Motor Cycle Club (UK) are now the keepers of the Norton dispatch records. They start in the early 1920s, when they give details of the date, frame and engine numbers, model, departures from original, and details of where they were first sent (the dealer, usually - so presumably yours will list Copes). That would be a good starting point, but would probably not add too much to the story of the bike.
If you have a log book with previous owner details, the sleuthing probably starts there.
Cheers
Leon