T206 Christy Mathewson Dark Cap variations/registration issues?

[steve B]

That's something that needs a bit of study.

The printing was certainly variable, even into the 1980's any color that was not a straight CMYK was hand mixed. The place I was at did stuff for at least two companies that used a "special company color" on all their stuff.
If it was mixed by a different person it might be different. (to avoid this the special colors for them were done by weight, so much blue with x of black, x of white, )

The inking levels and water levels matter, the Piedmonts with blue between the close together lines were ones where they were run a bit dry so the plate didn't reject the ink.

and the print areas wear down over time, which may tend to make things like the text wider within the letter. (And that's poorly phrased... )

Bu there are differences that are not really from anything like that.
I use Dygert as the example, because it's very clear that some have bright red on the lips and some don't and both are common enough that it's not a matter of a missed color pass, but a deliberate choice to not use the bright red on his lips.