Yes something like that
Usually there are groups of them so chances are that someone wears your armor.
A more advanced approach, though I dont really know if I considered everything:
Make some sort of self-learning system.
List A: Contains factions
List B: Contains a list for each faction, containing items ever worn by this faction.
A is initially empty, B has to be prepopulated with empty lsits since you cant create them on the fly (but make lets say 30 or so and you should be safe)
Then, a script is running in the background, ref walking all actors every 10 seconds or so, and for every faction they are in their worn armor is recorded in the respective list.
Edit: If getting all factions an actor is in is not possible, you would have to pre-populate list A.
Also, since this system would never forget anything (which might not be desireable), have recently detected items moved to the front of the list even if they are already in it. then, every 10 minutes or so, the last element is removed, so "one-timers" will be purged eventually.