I have never been given an explanation on why the SO was stamped in to the early cars instead of the vin - I know it dates way back in time - would have thought the VIN was assigned when the SO number was - but I do know the Feds had something to do with the mandate to stamp the VIN/partial VIN later - 68 or 69?

I'm guessing it was just the way someone set the process up back in the day and left it that way until Uncle Sam got involved in anti-theft regulations.

I know we have rigid process standards dealing with re-stamps of vins and such when a vehicle fails the rolls test and a trans or engine has to be replaced in the plant or before retail sale.