Nope, they're actually pretty common. usually they're small enough they don't stand out, and they aren't there for all colors.
They're registration marks of some sort. Usually today those are put on the sheet margins. It's also possible that they are marks left to help lay out the lithographic stones so the setup is consistent.
I've found a printing museum that's local to me, and I'll be heading up there with a few questions about the process as it was back then. I'm pretty familiar with lithography in general, but the exact specifics of how the work progreesed are only familiar for the era I worked in - late 70's early 80's. 1910 would have varied a bit and things are very different now.
Steve B
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