Nothing is “on” any individual MagicBand - it’s really just a gateway to whatever is in your My Disney Experience account - be it park tickets, a resort reservation, etc. Unless you or someone else has manually deactivated older bands (not a very common thing to do), any MagicBand is ‘active’ and ready to do.
If in doubt, on Disney’s website click My Disney Experiance —> My MagicBand and Cards —> scroll to the bottom Manage MagicBands and Cards section to see the status of any MB connected to your account.
Hope that helps.