while we check the stock requirement via MD04:the total available stock is 4,but there are 3 delivery order scheduled wi

while we check the stock requirement via MD04:the total available stock is 4,but there are 3 delivery order scheduled with total qty 20.why current stock is below than scheduled delivery qty.two possible reasons what I thought:1.ATP check is not working while delviery,that means delivery order was created disregard of short stock.but I checked checking rule for delivery and it looks ok.2.when delivery was created,there were enough stock,and some stock was issued to customer or some plants.so current stock looks short.but I checked the material movement document,there isn't special movement type(such as scrapping) and just have normal goods issue/receipt/return.so I am wondering where the stock was going.why current stock 4 is below than scheduled delivery qty since I didnt' see any special inventory adjustment/scrap?any idea on this issue.Thanks for any idea.