Anne, did you ever privately message the person? I'm sure you did but sometimes they've gotten it but forgotten to register, or couldn't read a # you wrote, etc. That's annoying though, at least that opens up a slot to send a new card!
I also expired ones to Belarus :( One of them arrived after 90 days more or less.Today I got a card from the US which had been "travelling" for 116 days! Take care!
I have hundreds of expired Postcrossing postcards, mostly on my Zmrzlina profile. They do drop off your board after one year, but they are annoying while they sit there and taunt you. However, as someone who gets messages nearly every day asking "did you receive my card ... I sent it along time ago and it expired," I do NOT recommend taking that action. Postcards expire for lots of reasons, not the least of which is that they got lost in the mail ... or the address is not readable ... or the postage is not correct (I know ... we all are CERTAIN we put the correct postage on our mail, but mistakes happen). Sometime folk just lose interest. Sometimes they have other priorities and just can't deal with anything other than the moment at hand. And sometimes they are registered after a very long time! It will drive you crazy if you focus too much on the expired. Let them go and send another postcard :)