Not quite the same issue but I had an interesting experience with the Royal Enfield Bullet I bought almost a year ago. Three weeks ago I booked it in for its first service and thought I should write all the particulars into my service book in readiness. I couldn’t find the registration document anywhere. So I went onto the DVLA site and entered my reg number to find that it wasn’t recognised!
Contacted the dealer who very embarrassed told me that they had forgotten to register it😳. So I’ve been riding it illegally for nearly a year and presumably with invalid insurance. The DVLA refused to issue the number or any other 69 plate but treated the bike as new so I now own a 12 month old bike that’s first registered in September 2020 and sports a 70 plate! I wonder if I can call it a new bike and therefore effectively get another years warranty?