Jim,
"A PORTRAIT OF BASEBALL PHOTOGRAPHY" is a wonderful reference in regard to stamping.
That said, as I have discussed in the past, there are fake stamps out there created to deceive that have been applied recently(not by conlon).Please refer to my comments on thread below.
http://www.net54baseball.com/showthread.php?t=193390
EDITED: By your description, I am afraid that you might be talking about a bad stamp. Below is a fake Charles Conlon stamp.
Ben