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.