Hi Ron
I do not find this unusual. I examined the Walsh card closely under magnification and it looked real to me.
This Powell is just another case of a printer's mistake. The printer was running PIEDMONT back print runs.
Followed by OLD MILL back run, in which he forgot to change the ink to Black. Realized his mistake upon
checking the first printed sheet and stopped the press. And hung up the Blue OLD MILL T206 sheet to dry.
Both Powell and Walsh are from the 150 series. In the future, it wouldn't surprise me if a few more T206's
surface from this series with Blue OLD MILL backs.
TED Z
T206 Reference
.