In the “Set Labels” drop-down list, active labels would be displayed at the top.
Gmail does it this way. In a label drop-down list, the labels which are currently checked (✓) appear first, at the top, followed by the rest of the unchecked labels alphabetically.
Makes it easier to see which labels are already applied to a passcard. Currently, on Android at least, a passcard's labels are listed along a SINGLE LINE. If the list of active labels is wider than the screen, some of the labels will not be visible and there's no way to see all of the labels attached to the passcard, except to show the “Set Labels” drop-down list and scroll through the whole thing, taking note of which labels are checked ✓.
This would be easier if the checked labels were automatically displayed at the top of the drop-down list.