6667ss138... this information may help a bit with respect to your overall curiosity.
For Norwood the production date was forecast in the production planning review meeting that occurred 72 hours prior to production. For those of you with "Echoes" on the book shelf have a look at pages 90-93.
Fortunately the production scheduling superintendent is still with us and I asked him about the vehicle shipper vs the production date.
He stated without hesitation that "the holding lot could hold better than 4000 cars at any one time and it typically took two days "or more" to get the car shipped". "Even more days were required if the car was held up at repair either outside in the holding lots, or inside at AGR".
"For vehicle shipping purposes the shipper must be very accurate as to the ship date when the shipper takes possession of the product. This is the "production date" as referred to on the shipper".
In a good faith effort to understand the relationship between the dates on the Body Plate (called the trim tag by the hobby) researchers and have tended to rely on the shipper info from NCIB and now the NCRS to establish the build date of the car and in so doing discount the date applied to the body plate.
OK: First off the shipper date is the date when the car was considered "released to the shipper" -- and all production/repair was technically complete. In the period 1967-1970 the date of production on the body plate in relationship with the ship date could be influenced by any one of the following:
A production hold at the Fisher body bank
A production hold off line at Fisher in body shop, Paint, hard or soft trim.
A production hold at the Chevrolet body bank.
Chevrolet repairs after production at AGR
Chevrolet repairs after production in the post production holding lots
My 1969 Z-11 fell right in with the description provided by the production superintendent. It is an 05-A Body plate car. Based upon the NCRS provided "production date" from the vehicle shipper-my car sat in the plant holding lot roughly three production days prior to being assigned a shipper date for May 7th.