Neat find Scott. I try to keep stats on all the reoccurring print flaws
front or back and I've never seen this one before. I checked past
Covaleski EPDG sales and of the six I found one of them had the
same mark as yours so that's two out of seven Covaleski's with
the mark.
Covaleski EPDG.jpg
This is just an opinion based on the statistics I have on several
print flaws but I think most of the non Piedmont and Sweet Caporal
sheets had fewer vertical rows of the same subjects for example
a Frank Owen flaw is found on 3 out of 5 EPDG's but the same
flaw is found on only 13 out of 152 Piedmont's and other flaws
have comparative statistics when they're found on one of the
uncommon backs.