The last 6 numbers of the VIN will not appear on the cowl tag. The cowl tag was stamped at Fisher Body early in the build process. The VIN was assigned after the body arrived on the Chevrolet assembly line. The VIN plate on the driver's side door jamb should match the last 6 numbers on the hidden VIN found on the vertical edge of the cowl under the driver's side fender. The cowl tag has no legal status. The VIN does and, in most jurisdictions, it is illegal to tamper with it or remove it.
I noted some of this in another threat but it applies here more-so. Fisher Body stamped out and attached the cowl tag based on what Chevrolet 'told' them they were building. Fisher built, painted and trimmed the body, firewall back, then shipped it across the tunnel in a 'mix bank' to the Chevrolet side who added fenders, hood, power train and chassis. The Chevrolet side and Fisher side of the plant were not exactly enemies back then, but never on good terms. They merged in 1984 and Fisher Body was no more. "gone but not forgotten" as the T-shirt reads. I retired from GM and went to the Willow Run plant in the late 1990's to inventory equipment for other plant use just after they shut down the plant. I invited some NNN guys along to tour the plant (empty almost) and have a sit-down for questions with several engineers and supervisors, several of whom there since the 1960's. The most important thing we learned was that the Fisher Body cowl plate was the PLAN, not the result of color and options out the door. The second most important thing, when we told them we were there to find out "What is factory correct" and they responded, "We ARE the factory. Whatever we did was factory correct - even if it was wrong" Can't argue that. They gave us some original photo off the office walls and an NOS L79 carb they dug out of a drained oil pit. A couple of these guys attended the NNN Nats in following years and amazed us at what we didn't know about the build process. I wish I had taken better notes.