scott - there are a many ways this could happen on press through poor quality control..... or simply during the initial setup (make-ready) for the run.
for instance.... all one has to do is run too much black ink (or not enough water) and you will achieve that plugging in (you call it shading). If a pressman saw that the black was running heavy, he would have adjusted and kept running. What you see is the bad printing that was fixed.
This is not a variation.
no matter if is on just one card, some cards, or all cards - this is a print defect..... as the issue can happen on the entire sheet or on a specific part of the sheet.
As far as printing plates....
and your mentioning "DIFFERENT" plate....
I mentioned this before -
Printing plates only have so many impressions in them.
I don't know the number of sheets that could be run off by a plate in 1910ish.... but I would bet it wasn't more than 10,000 sheets - probably less.
To compensate for the short life span of printing plates - multiples of the same printing plate are produced.
So.... for just about any mainstream card we collect - - there were MANY plates created for the same card. As plates outlived their usefulness, a pressman would take off the bad plates and put on the new (but same) plates.
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Joe D.
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