So, we have something telling us that we own an item when we look at an NPC shop, which is super useful! However, we don't know how many of that item we own. It might be 1 or it might be 100. I think it'd be super useful (especially for restocking for quests, which is highly encouraged nowadays) to have it display somewhere how many of an item we have.
I don't think we really even need to worry about how many we have in storage or in our shop, just the number in inventory would be plenty (or all of them, depending on how the database is set up, just whatever is easiest).