That is not true about the stamped postage. If it has a date on the stamp, it must be used in two days or it isn't any good. My postal workers have been good about honoring the ones that have been sent to me. They are not happy about it, but they do it as I am a very frequent patron. There is a flat rate stamp that has the Mackinac Bridge on it (I have used almost 60 of these for the last swap that I did) and it costs $4.90. It is a Flat Rate Stamp, that may be what the confusion is. it is used on a flat rate envelope, which is NOT the priority envelope. I will take care of the envelope. All I need is the stamp. I can get two sets of blocks in an envelope. Just make sure you also send a large zip lock bag for the return blocks.