You will get stamps from two different people once what you have sent has be registered as » received » I made the mistake of thinking that I would send stamps and get stamps back from that person. It may be possible at sometime you will get stamps from someone you have sent stamps to at some point. Otherwise, it’s supposed to be .
I would think that they are referring to Post Office generated « labels ». As I collector, I prefer to have actual stamps on envelops. I was recently admonished by an exchange partner who was not pleased to see such a ´label’ on the envelope I had sent. My reply was that I have no control over the stock that my local postal outlet has on hand. The letter in question cost $5.90 and there would not have been enough room for 5 $1 and the further additional stamps.