I think this the most definitive answer we'll ever get on the topic or IRC stamping - I wrote the Universal Postal Union, UPU, the organization that makes them, and below is their answer.
Now I have to bring a dozen back to my local post office to prove I was right and to have these fixed...
73, Walter W2WJO
Subject: RE: International Reply Coupons From: [EMAIL PROTECTED] Date: February 12, 2004 9:57:11 AM EST To: [EMAIL PROTECTED]
Dear Mr. O'Brien,
The originating post office who sells the IRC stamp their postmark on the left side, but it is optional.
Regards,
Claude Voirol
Mail Programme Assistant
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