Today I got a card from Germany where one digit in the ID was missing. So, I tried to find out what the missing digit might be, by playing around with the ID and accidentally registered a legitimate ID of another card that was sent to me as well. Oops!
I’m sure I’ll get this card soon, but the ID for the card I have actually received today I still don’t know. Have asked Postcrossing now to find the ID for me. Do not want to unwillingly register more cards that are still travelling.
Consecutive digit cards aren’t all that uncommon. Something to do with the Postcrossing algorithm and how many cards you are due and so on and so forth I guess.
Just blindly guessing at a missing last number in an ID could be more likely than most people think to end up in a “false positive.”