The scheduled production date is just that....a SCHEDULED date. Cars were built earlier or later than the scheduled date for a wide variety of reasons. The actual assembly can be no earlier than the latest date coded part. Some package cars (A12 6bbl cars, Superbirds) only have one or two SPDs but were built over time.
Some broadcast sheets appear to show an actual construction date.
Once the MONTH YEAR safety sticker come into effect, one can find instances of the SPD being in a following or previous month.
Sales bank cars were a way to keep the line moving between ordered cars and to have some inventory available for dealers.
Agree. Every assembly plant had an area between the paint shop and final assembly where finished bodies were stored. A body could exist in this area for as little as a few minutes to as much as a few weeks.