Ill be kind and just believe that you havent paid attention, instead of intentionally defending the fraudster in chief.
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If the Selective Service form is authentic and it belongs to Obama, I have trouble believing that the postal worker who stamped the form---I would guess that he used that stamp many, many times on all kind of federal government documents and not just on Selective Service forms---would not notice right away that the "19" was missing on the stamp on Obama's form.
That is, I would think that once the postal worker saw that the "19" was missing, he would stamp the form again to make sure that "1980" was stamped on Obama's Selective Service form like it was supposed to be.
Postal worker's supervisor: I don't think the the postal worker's supervisor would have been too happy to accidentally find out later that the postal worker did not stamp Obama's Selective Service form correctly, because how could the supervisor ever be sure that the postal worker did not make the same mistake on other government documents and on other Selective Service forms?
So I believe that the postal worker would have re-stamped Obama's form in order to make sure that "1980" was stamped on the form correctly, because I don't think he would want to get in trouble with his supervisor and possibly be punished for his mistake like maybe losing his job.
I may be misunderstanding your post but, no postal worker stamped anything on this. Obama and his ilk forged this document.