You see some of this in other products. I think some of the varieties of Nintendo 3DS had different screen types, with no difference in model number; have to open the box to see what's in it. It's generally called the panel lotery; some purchasers will return a device if it doesn't have the panel they want and there's no way to specify.

Apple could split by model or destination market if there's a significant difference in quality or price, or just shuffle and you get what you get (or you return it until they change the return policy)