Comment on Apollo 15 postage stamp incidentparentComments−meemo7yAccording to https://en.wikipedia.org/wiki/Event_cover they are "decorated, stamped and canceled commemorative envelopes"Essentially they are envelopes with stamps and a marking over the stamps that prevents the envelope and stamps to be used.https://en.wikipedia.org/wiki/Cancellation_(mail)
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According to https://en.wikipedia.org/wiki/Event_cover they are "decorated, stamped and canceled commemorative envelopes"
Essentially they are envelopes with stamps and a marking over the stamps that prevents the envelope and stamps to be used.
https://en.wikipedia.org/wiki/Cancellation_(mail)