I think the CMs are still learning what can and cannot be done with the MagicBands. The first day we were here a CM at one of the FP+ kiosks at Hollywood Studios told us that our PAPs could only be active on one MagicBand at a time. This is not true, or at least not true in our case.
That is definitely not true. Park tickets--including APs--are not "on" a MagicBand. Ever.
Going forward, the MyDisneyExperience account is the hub for data storage. You link your park tickets to that account. With things like non-expiring tickets, it could store remaining admission counts for years and years to come.
The MagicBands are also tied to the MDE account. And that's how the link is established. When any MagicBand on your account is tapped at a park entry gate, it queries the MDE account to validate admission. Nothing is ever stored on the band.