How did Barry determine that the SPDs were only 7 days apart and that they were 10 away from each other on the line? Does that info show up somewhere on the build sheet that I found?
By comparing the three data points on the two sheets. Both sheets list an SPD, a VIN and a sequence number in the first box on the top line.
As with fender tags, different plants handled the sequential numbering of broadcast sheets differently. My area of interest is the St. Louis plant but if I recall correctly, the Hamtramck plant numbered sheets using consecutive sequential numbers. Barry compared this sequence number to determine the number of units apart. I’ve not looked into sheets from the Jefferson plant in detail but I think Jefferson used the same method. This method provides a much more reliable relative build sequence comparison than anything else. Remember, plants handled sheets differently. What happened at Hamtramck didn't happen at St. Louis and both may have been different than Newark.
Let’s try this example. Car A has a Scheduled Production Date of March 1 And a VIN of 200000. Car B has a Scheduled Production Date of March 11 and a VIN of 210000. They are 10 days apart and 10,000 apart in VIN number.
If one, erroneously, uses the VINs as a comparison of relative build, it appears that the cars were separated by 10,000 production units and 10 calendar days. Thus method assumes a consecutive continuous production flow but we know cars were built before and after the SPD and out of VIN order. We know this by comparing invoices, shipping info and other documents as well as the dated door stickers that came about circa 1972 model year and later.
Car A was ordered by a dealership with a known record of slow payment and is 'on notice' from Chrysler that payment upfront is needed before construction of any cars will begin. The construction of that car was delayed one week, seven days, while Chrysler waited for payment before they would start building the car. If we use the March 1 SPD date as an actual date that construction should have commenced, this now puts the actual start date of car A on March 8th.
All of the components for car B are on site. It's paid for and a customer is waiting. A shipment of model specific sheet metal does not arrive at the plant due to a winter storm leaving a gap in production that leads the plant powers to be to say "We don’t need to wait until the 11th to start this car. We’re ready to build it on the 8th. Let's get started." This means assembly begins on the 8th, three days before the SPD as well the same day as Car A.
Before production starts on the 8th, broadcast sheets are printed at various stations for that day’s actual work flow. The SPDs (301 and 311) and VINs (200000 and 210000) of the two cars are printed on the sheets as they were originally assigned well as the timely (printed on the 8th) and accurate sequence of numbers (say sheets 208001 and 208002) in the top left box.
Both cars are “on the line” the same day; the 8th. The are sequenced one car apart. Both go through the trim shop the same day. Both cars have the same P6X interior. Line worker Bob grabs the back seat destined for car B, along with a copy of the BS for car B and installs it into car A. (Remember, they have the same interior. Bob does not need to check the sheet against the VIN because all that matters is Bob puts the correct back seat for a P6X interior in a car. It's not a requirement that Bob puts one specific seat in one specific car.)
Fifty years later, I find the sheet for car B in my car A. If I compare only the SPD (ten days apart) and VIN on a broadcast sheet to my car’s Fender tag (10,000 units apart), and not the sequential number of the BS, what might I, erroneously, conclude?
This is how wrong sheets wind up in different cars. Cars were not built in VIN order. This is why VINs and SPDs are, virtually, useless in determining accurate construction sequence. VINs are unrelated to construction They are administrative. The DMV cares about the VIN. The people that built your car, probably, didn't. VINs serve a different purpose than assembly order. This is also why every scrap of documentation is important in learning how things were actually done at the plant. Save sheets, save window stickers, save fender tags.