Why do you doubt that the Piedmont Plank's are proofs ?
All 3 Plank's we have accounted for in this thread have the identical proof mark on the top border as does this repro
example of the Eddie Collins' proof.
Here's a "twist"......perhaps Collins, Plank and Wagner were all on the same sheet. And, when American Caramel Co.
prevented American Litho. from issuing Collins and Plank....Wagner was discarded in the process. I find it more than
just coincidental that the same number of Piedmont Plank's equals the same number of Piedmont Wagner's.
TED Z