Yes that was great foresight on the owners part when it was wrecked. But really, how many people actually think of that? Not many. They are just happy to get their car repaired. As far as engine and trans matching numbers that only started in 1969, so prior to that having an engine and trans with casting date numbers prior to vehicle build date is usually sufficient.
What about warranty blocks. They are in demand. The vin partial pads are machined, but no digits stamped. So if your high dollar resto project is missing its date coded block, do you find a warranty block cast 1 month prior to your car build, and stamp your vin partial on it, and use it, or look for a warranty block cast a year or 2 after your cars build date and pass it off as a warranty block with no numbers but correct for a resto?
I would say scenario #1 is fraud, stamping the vin partial in a warranty block to pass it off as original. Scenario #2 is prob legit, any number of these cars were run hard and blown up, in this case its entirely possible the original engine could have been destroyed and replaced under warranty.