If you got the serial number, you could get bogus reggie.
If the collector has lots of bikes, often they are in storage or storage units.
If someone picked up said bike at the storage unit or place of storage, by whatever illegal means.. They are now driving away with a bike with papers..
Now it is a simple matter to take it to another state, or even overseas, transfer it into another name.. now it gets much harder to recover...
If there is a market for Rodans Rembrandts, etc that are hot and you cant take out in public.. then there surely is people that would be happy to "own" scarce motorcycles.. Brough, 36 EL's, Vincents, Boardtrackers, Indians, even early Honda fours..
Real 36 EL.. 70-100k.....hot one you can only show your buddies. maybe 20 K.. or it gets parted.. and they toss the cases..
That is the problem, as I have been brought to understand, through the AMCA type of guys..