It's a puzzle.
What would have been done would be a pasteup original of the cards (Or the photos), which got photographed through color filters and a screen.
Each color for CMYK would get it's own negative, so blue spatter inside a blue area like the Aaron RB wouldn't be a surprise.
Any spatter of anything on the blue negative or the original would turn up on the plate. But spatter on the negative should turn up as white spots.
At the shop I worked for, the camera guy once shot an entire job right after both a liquid lunch and "cleaning" the camera room - which mostly stirred up dust. I got to spend a couple days in the stripping department finding spots and fixing them with some stuff like red whiteout. And that was nowhere near as bad as these cards.
I suspect some spatter in the developing of the negatives that left blank spots on the blue negative. It's pretty bad they let that through.
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