Hi All .. Apparently over the years there has been numerous secret chassis/VIN locations discovered on various General Motors products in the USA by motoring enthusiasts over there. Only the factory and authorities had access to these secret locations originally (for obvious reasons) and are nothing to do with normal factory codes.

...My own experiences of this secret numbering has been a 283 Chev engine I still possess with the engine number also stamped on the machined fuel pump face (in smaller stamping), along with the chassis number of a Peterbilt cabover semi that I own with, once again, a smaller version of the chassis number underneath the pogo stick mounting crossmember.

...Has this practise been carried out on our GMH vehicles ? .. and if so, can anyone give an example of this practise and what they have discovered, Cheers.

The tag number continued on VT-VZ as well, but moved from below the headlight and onto the brace for the LHF bumper side hanger.
Easily removed though, as it's only rivetted on.

Not many seem to know about the VIN being stamped (dot matrix) into the floor of the later ones either. Many assume the tags is all they have.

Part way through VN (when the PBS was phased out) they started putting stickers on major assemblies like the console. The stickers contained the tag number (last 6 digits of the ISOVIN) as well as pertinent info about the part identity. It also had the trim level, sequence on the production line, and the date/time the assembly order was raised.
These stickers spread to more (and also more basic) parts as the years progressed. VY/VZ even have them on the inside of pillar plastics & dash end caps.