Well, yes, I think they save the stamps. And each of these were also sold individually, so that if you wanted to send 10 invites to a wedding you could buy one sheet of 10 “Ja!” stamps. The collection sheet was another option. I bought several sheets of the “invitation” stamps because they feature cake and sweet treats. So many people like cake! I sent those “Einladung” (invitation) stamps to lots of people before I ran out. Nobody got confused and showed up at my house thinking they’d been invited to something!
I think I would also be careful about when and where to send that stamp!