Thanks eyeonwall. I have heard of this from mounts but I think GrGDad called it mount flash but being the same. He said a lot things goes on behind the scene in the stamp books that people don't think about. Air and lack of, chemical decomposing and so...sounds too scientific.
Back to the punches now. I've been combing the back of a lot of stamps and noticed that I have not seen these punches on any other stamps except this issue. Could it be that the punches are common for the Pan Ams but not common for other issues. If any of the family here has them on other stamps please show a scan and if you have any Pan Ams with them please post scans as well I would like to view them. Thanks Newby