Unless they changed how inventory commingling works, you might even get a counterfeit item when ordering an item that's sold and fulfilled by Amazon. That could happen because they consider (or at least considered) items with identical catalog id to be identical, so if for for a given item id, its "Sold by Amazon" inventory is empty while the FBA (sold by 3rd party, Fulfilled by Amazon) is not, they might "lend" one from the merchant until restocking their own inventory.