I think partial vin on block and trans requirements started for 69... Idk when the law was signed, but on something like that they almost always put the effective date somewhere in the future to give manufacturer time to get set up for it ...
Just like obd-2 was mandatory starting in 96// but some vehicles came set up for it in mid to late 94 already.......
The link in post#11 has notes & a link to the actual gov docs as well as other sites, & it seems that they all started with the "Hi-Level/Option" cars a bit early, then got around to complying with the run of the mill fleet.
I know the GM Cavalier/Sunfire cars had the setup for OBDII when that body made it's debut, but wasn't actually OBDII.
