Rum world.
I the 1960/70s I'd buy a van load of bike parts, this craze for numbers/orginality had not started back then. I'd build up a bike from whatever bits were there, sort out a logbook to suit and use that reg.
After a while I'd return the old buff logbook for a change to the engine number, back it came duly adjusted, them may be a year or so later ditto with frame number;sometime I'd be asked to bring it to County Hall for inspection,sometimes not. Bingo everything matched the book.
Not really dishonest, as the bikes were not intended for sale and half the time the bike got returned to my shed as parts.
There are a couple about though, one an AJS/Matchless allsorts had bit of BSA, Triumph and several different years of AMC. Engines went from iron to alloy and back again; Last I saw of it was in Bristol in the late 80s, the number I registered it under had been sold off and now lives on a yuppy mobil in Scotland.
Was it a fake? not really, it was a bike of my own creation, did many many miles on it including a trip to Spain. Only sold it due to changing circumstances. Joke was on me because circumstances changed for the better not the worse and I wish I had it now.
So all this feitish with numbers amuses me no end; did Norton actually have matching frame/engine numbers? AMC did not.
Engines get changed over 50 years, so I'd say if the numbers in the V5 match those on the bike, and you got the cash go for it, values are not fixed so who can advise on that? you may get a dog, you may get a gem. That's life.
Personally I think old Norton twins are fugly bikes and wouldn't give one shed room unless it was a freebie
