Mike
See, staying in school and sticking with chemistry and science has paid off for you.
I would agree 100% with the statements above as accounting for color variations.
The different paint mix batches say a lot for the different shades of argent found on NOS 70 Barracuda grills and headlite doors.
I know we're talking assembly line here, but NOS, over the counter items were still painted using the same formula in the same facility.
In the early 80's when Downer had most of the NOS E body parts locked up, I recall buying boxed NOS Barracuda grills and headlite bezels all the time at shows, through dealers, and in Hemmings.
We'd gather at Downers in NJ say for the Englishtown show, and he would pull out no less than 10 NOS boxed grills and h/light bezels. We would compare colors in the light trying to get a matched set so everyone had a close mix for their car they were to be installed in.