I have a 1967 coupe barracuda with a low serial number and shipped march 1966.

krazykuda said
Pilot cars are built on the assembly line...

They make a run of PVP (pre volume production) cars about 6 weeks before model year launch that are supposed to be built with production tooling... All parts are supposed to be made from production hard tooling... Any parts that are not off production tooling must have an approval and be certified that the prototype part will be as good as the production part...

The purpose of the PVP builds is to test run the supplier's tooling and parts and also to test the production line tooling and fixtures to make sure that everything is ready for production launch.... This way they have 6 weeks to get any bugs worked out that they find on the test build...

You said it your self, pilot builds, are made shortly (6 weeks) prior to serial production, the original poster was talking of a car assembled 3 months (12 weeks) early.
Also those ‘pilot’ build strategies are problem detection tools that are used today. I wonder if those were even employed by the big three 50 years ago. I certainly did not see much of that when my automotive production carrier began in the early ‘70’s. Having all components off production tooling and fully verified was not really implemented till the 80’s. You seem to be trying to apply today’s best practices to the late 60’s Detroit build methods.