unrestricted use quantity is not the same as available available quantity
available is only that part that is not reserved and not included in sales orders and deliveries.
MMBE has some more columns than just the unrestricted use stock, a double click onto a stock line will give you more insight, will tell you how much is reserved and scheduled for a delivery.
if you want know more about available portion of your stock, then check MD04 or CO09 transaction.