Okay, then his research is to be considered fact? It's the result of careful research, but it would have to be backed up with broadcast info for every sheet.

Here are a few questions that will help make or break the theory.

How did production schedules run? If a car is 10E, does the build week include the entire week even though it picks up the first few days of November? If a car is 12A, does that week begin on the first day of the calendar month, or the first December day of a production week? And is a production week Sunday - Saturday, or something else? And are these cars from normal 1968 production year, or extended (late '69) production?

Comparing a perpetual calendar to the production info will give a better view.