From my experience of three cars and one account, I found that any valid SD card could be updated. After your vehicle is sold, the new owner will update it on his/her account. None of your personal information will be transferred.
We bought a new CX-5 and started an account with its SD card. We then bought a 6 and used the account for both cards simultaneously. We then sold the CX-5 and bought a newer but used CX-5. Both cards from the current cards are accepted by Mazda Toolbox.