My car's door sticker is April 1970.
An unrestored twin 2 VINs past my car was in my area until recently. Too bad it was sold as it would be interesting to see what the date code was on its spare. If I run into the car's former owner I will ask him where his car ended up. Anybody know of a recently purchased unrestored red Mr Norms T/A being bought last year?
Having been an engineer in manufacturing most of my career, I do roll my eyes a lot when I see people trying to nail down what date code part is correct for their car. Certainly there would be an "on average" date, but if you were able to document each and every car right after build, I'm sure you'd find dates well outside of what you'd expect to see.
Keep in mind too, date codes are a quality control thing, they are not like a "use by" date on a box of cereal. No one at the plant cared or paid any attention to what date codes were on the parts they were installing.
I've personally called plants to have some parts sent to me for testing or evaluation, and many months later returned the parts I didn't use to the plant, as an example. I'm sure that happens at most manufacturing plants including Chrysler plants 50 years ago.
Inventory control is pretty good today but parts still end up going to the wrong place from time to time, and it might not be until an inventory months later where things get back where they belong.
I'm sure this situation was worse years ago, before inventories were managed with computer programs, and parts bins labeled with UPC codes etc. I would guess people managed the inventories with hand written ledgers then? "Just in time", "Kanban" etc didn't yet exist 40 or 50 years ago either I don't think, so parts management at plants was more inefficient then.
I work at a truck manufacturer now, and I know trucks come off the line often missing parts, they get towed to a storage lot until the "test and tune" department can fix it, which can take weeks. Trucks are more customized and much more variability than a car plant, but still, I'm sure situations where cars came off the line with missing parts or something else wrong and must be fixed happen now and happened then, all the time, so a part might get installed on a new car weeks after a car's manufacturing date at the plant.
Unless you could go back in time and inspect and document your car at the plant you can never say what date code was on a part on your car. That includes my spare. My car sat at Mr Norms for nearly 10 months before it was sold. Whose to say that in that 10 months, they didn't need a space saver for a car being sold or a customer car being serviced, and took the spare from a car in inventory, which turned out to be the one I eventually owned, and then replaced the spare with another one, the one in there now?
So again, you can document and study this issue to death, but in the end, it doesn't change the fact that any individual car built could have rolled off the plant's grounds for the first time, new, with a part that could be date coded 6 months or more before build, to even a week or several weeks after build.