[taming]

This also works for Joanna because her mom does not want to have anything but books bought through Joanna's account and applying the DRM though Joanna's ADE account on her device. You can load the same books, bought with the same account etc on the six devices (and six computers) with ease, but each device works with only one account at a time.

If Joanna let me plug into her account, the DRM encumbered books on my reader bought through my own account would convert to "locked content". Removing Joanna's book would magically unlock my own once I reauthorized my reader with my own Adobe ADE.

I believe other DRM schemes like kobo kepub (their own DRM) or Kindle DRM, does similar things--one device, one account. Kobo does this by only syncing one account per device. Sync with account #2, and all the books on your device through account #1 magically disappear. They can be reloaded when account #2 is gone from the device.