Associating sales orders and products

Associating sales orders and products

Our company sells ad space in different publications. We use sales orders in order to keep track of which ad spaces have been purchased in which book. Right now I am trying to link the inventory of a product to the sales orders requesting them and failing pretty badly.
For example:
The product is 08TNWFFull. There are 6 possible spaces. 3 sales orders have come in requesting 08TNWFFull be set aside for them, but the inventory number isn't changing after completing the sales order-- it still says that there are 6 in stock. The product info also says that there are 0 ordered and there is 1 in demand. I thought that after the sales orders were completed for this product, that there would be 3 left in stock and 3 ordered (or perhaps even 6 in stock and 3 in demand).
What am I doing wrong? It may just be that my business inexperience is showing ( ), so any help on the matter would be great! Thank you!