Item stock and restocking

I've noted that the Dark Swords in Belvast restock every few minutes(I'm personally guessing 10 minutes because that's the same time as price change, I'll be testing it later). The swords restocked back to 6, and the other items added more stock onto them, so it might be individual for each item. Also there's a possibility that the stock is shared between all channels, I have no idea how that would be tested though. I saw that the Dark Swords ran out completely while I was looking at them, but I didn't notice anyone else nearby who could have bought them(it could admittedly been a lack of attention on my side though).