This might be a ways off (or I have asked already) but I'm curious if that ID code correlates to the card restore IDs in TEST. I know that when one of my cards was corrupted, I was able to restore it from one of the IDs that was in TEST. Huge leap in assuming that ID is probably only used for restoration purposes considering that the times/story status are loaded from the current card that is loaded and the saves are only written to the card before stage selection and after stage completion.I put together a blank ID4 US card based on my logs. I edited the ID code to be FF FF FF FF and successfully simulated purchasing a new card with data written to my card file!
The game does not appear to care about the ID. It doesn't appear to be informing any kind of stored checksum or anything, so the good news is that a random ID should be possible in order to make unique cards. This will be needed if it turns out the game tracks cards based on ID. If it doesn't care about multiple cards with the same ID, then this won't matter.
At least for ID4 US a blank card appears to have specific data in the header, including counters, and then everything else is filled with FF. I haven't gotten into attempting something similar with ID5.
It might be that the latest card data for so many cards gets stored and there is some kind of verification process that checks that counters are the same or less than the saved data, and maybe it compares some other data to prevent tampering, but it has to allow for some changes since a card could be run in a separate machine and changes made/counters decreased.
At any rate, even if the card is stored based on ID, the act of restoring to a new card (or even transferring to a new card upon expiration) would change the ID.
It remains to be seen how robust the backups and verification processes are. And I can only test in ID4/5. Newer games may be different.