If I Have A Block And Use Stamp Hinge On The Border

I slap at least one on every envelope that I mail for decoration and/or conversation starters.

Very good idea!

Similar things have already happened in many countries. Consider every country in the Eurozone; mint stamps in the old currency are all worthless for postage now, and you can pick up nice MNH assemblies from the 1960s to the early 2000s from those countries for pennies per stamp. Papua New Guinea doesn't accept non-current commemorative stamps for postage, IIRC, and there are probably other countries that have similar rules.

Heck, United Nations stamps are still technically "valid" for postage, but since they don't allow people to send out bulk mail or large packages from the UN post office anymore, those stamps have lost most of their postage value. You used to be able to sell bulk mint UN to NY-area heavy shippers for around 20-30% face, good luck doing that now!

I have a several lifetimes supply of unused U.S. postage stamps that USED to be MNH plate blocks before a broken water pipe in 1968 put 2 inches of water on the floor where I had them stored "safely" in a footlocker.

Today I use white glue to attach them to every envelope possible. I've even started paying bills in large manila envelopes instead of the ones included in each statement. It surprises the recipients (and the postman), and gives me another reason to stay alive. That makes my wife happy.

I have yet another lifetime of perfectly good MNH plate blocks and blocks of four that are duplicates. No, I'm not interested in the hassle of operating an ebay store.

Some of the stamp auction firms for years have been mailing out their catalogs using tons of mint stamps as postage .But I agree with what has already been said that the Post Office is going to invalid all old postage stamps for mailing .