I didn't mean to imply that you could redeem them at the post office. You can't even redeem (refund) current stamps. Sorry if I didn't make this clear. The point is that stamps never lose their face value (if unused) and even a 1 cent stamp from 1900 can be used today.

This is one way the USA is different from virtually every other country. Other countries are like Las Vegas casinos: their money can expire.

(I'm not sure - maybe others can correct this - but I think Switzerland - at least since 1900 - may be the only other country that has not invalidated or revalued its money. Canada would have counted except they devalued the paper dollar a couple years after the Loonie was introduced)