The MIB2 cards at least have a hidden partition on them, they are special SD cards http://www.seatcupra.net/forums/showthread.php?t=388586&page=26 It was notabenem in November started this one off in post 501 with those key filenames. Then it was Exciter that found the patent to the storage method of the files in post 525. That NDS file. It's the CID which is cloned if an additional card is made but isn't required unless you are worried about messing the card up. It's the CID which is out of range of a format or delete and it's that which marries the card to the unit. https://richard.burtons.org/2016/07/01/changing-the-cid-on-an-sd-card/ That bit was covered in Exciters PDF but isn't required if your not manufacturing a new copy of existing card linked to the unit. Notabenem 1-3 are the only things required as long as a copy of the original SD card is made before reformatting it. The CID isn't important since that doesn't get touched in the format. Why the NDF business works I guess it's something like having the top level index, that's linked to the database release on CID but works with the updated map data that is indexed from the top level, which was probably an oversight in how they thought it was locked down. The front page of the phone book works with each update even thou the pages below change. You got to respect the geo information system programmers who were looking at the card.