Waiting for an invoice

There is a fix for improvement. If in the order, where we receive the goods, there is more or less than the quantity indicated in the process, where it is necessary to reserve - what will happen? It is necessary to reserve the maximum possible amount of goods. That is, if we arrive 10 pcs, and in the process where we reserve 20 pcs, 10 pcs should be in the reserve, and vice versa, if we arrive 10 pcs, and in the process where we reserve 5 pcs, 5 pcs should be reserved.