From what I understand its unfortunately not by who orders first but rather by which store your online order is placed with and how efficient they are in filling that order. For those who ordered online, there was quite a varied postage cost which would be due to which store the order is being filled by.
Getting the order in is one thing but having it fulfilled is another as the stock in each store is limited so online orders have to be filled from what's on the shelf and in the back which means if your order went into store with 5 units and before someone is able to get around to fulfilling the order (physically taking the item off the shelf/back) those 5 units are either sold in store then the online order can't be finalised from that store hence the out of stock email.
