Delivery Qty and Date confirmation

Hi Experts,

If material stock is not available in plant and if there is NO Incoming (on order) P.O. and NO Production order also

What is the logic system will confirm the stock and how system will confirm the delivery date with confirm stock.

I am trying to analyse one issue

User created on sales order on 18.01.2011 that day system confirm the QTY and delivery date as on 18.01.2011 and user have that output screen shot (sales order confirmation) and practically there was no stock available in system

Later on now system shows the confirm QTY and DATE on 22.02.2011 for the same material and shows in output also.

My question is why and how system confirm the delivery QTY and Date on 18.01.2011

Best regards

Hanumant