The x30 series downloads work as follows
1 - Jepp subscription which you log onto using a Jepp Updater application
2 - Updater Application tells you how many downloads you have left for the current cycle (based on how many you have bought - eg. for a dual GPS configuration)
3 - Download the file (which I believe is encrypted) (you can download and save or download and programme directly. Once the download is confirmed your account balance (held online) is debited.
4 - Decrypt and programme the card, once this is confirmed the file is deleted.
You can program any card with your account and use it in any x30 GPS.
Only on very rare occasions does the process leave you with an invalid card and no credit to try and programme again.
I have not poked around in understanding the security of the data once it has been downloaded or understanding exactly how the system updates status to know that the file has been downloaded or that the file has been programmed.