Barry
How about this for a theory, the production line uses all the parts that are on one rack, when finished they move onto the next rack? Clearly the important things need to match the build sheets, but I can’t see good parts that will fit not being used. I also doubt that the Factory Manager gives any spares to the Parts manager to sell via Parts, they both need to show good profitability and that may be considered as the most important factor for their bonus.
Also, with the intro of a new spec sometimes suppliers are late to change over, so to keep production going the Management and Engineers may have to build a few in between specs. I think Jaguar are famous for a series 1.5, or perhaps 2.5 E type.
And / Or, yours was part built pre August shutdown and then then finished, repaired post summer. The gap may have been several months. FYI I was once the proud owner of a new car which showed many signs of having been cut n stuck prior to me receiving it.
Out of interest does yours have a ballast resister for the coil, or ballast built into a resistance wire that looks a bit like a doorbell wire?
Mine is Dec 1973 build and is a series 2 with many differences to the series 1.