Does anyone know which script causes NPCs to automatically reevaluate their equipped gear? And which one causes them to reequip outfit items?

Say for instance an NPC is given a new piece of equipment through a script such as:

thisActor.EquipItem(thisArmor, true, true)

Which vanilla script is causing them to reevaluate their current inventory? I have an issue with a script that adds items to the NPC and also removes an item from them. Unfortunately if the item I remove is part of the NPCs outfit, the outfit piece has a tendency to magically reappear in their inventory. So does anyone know which vanilla script causes an NPC to equip an outfit item and also which script causes NPCs to reevaluate their inventory upon receiving an item?

Best Regards,

Nightasy