For point 4, I'd like to add that the player would surely have a preference for discarding stolen goods instead of owned ones wherever possible. For example:
- If you're poisoning someone or giving them a live grenade, then there's no reason not to use the stolen one.
- If it's just someone's sweetroll and you're giving it to someone else so they have a nice surprise snack when they check their bag (or some other totally arbitrary reason and item) it shouldn't make much difference that it's stolen.
- If you're trying to put something in another NPC's inventory because you know you're about to be searched by guards but the other NPC won't be, you'd want to get rid of the stolen one.
- If you're trying to frame an NPC for a crime like in Skyrim's first Thieves Guild quest, you most certainly want to reverse pickpocket the stolen one.