I have a few of the pink ones, (Actually the Magenta from the CMYK) And they are definitely bright pink. I've actually sought them out at times because I think they're a bit harder to find.
I have some boxing too, and haven't seen pink on any of those.
It's a good point that boxing was 48 and continued into 49, so that makes the pink ones a bit more of a puzzle.
The inks would have been mixed by hand by the press operator. Starting with the basic Cyan Yellow and Magenta different colors are made by adding a little of other colors. Usually enough is mixed for the day or shift, or if the job is small, by the job.
Like the blues, they all start with the same cyan base, lighter ones get a bit of white, darker a bit of black.
The darkness/lightness seems so far to match with the particular plate differences, so I don't think they're mistakes other than just plain sloppiness.
Why they would just use the Magenta straight when they'd been mixing red for a while maybe even a year or so is a mystery.
The transitional types where they have one type for a couple colors and a different type for another are actually quite hard to find.
