Kim gave you one smart option,and that can work. The tricky part about using the order archive is that it can have several revisions of the same order. So what version do you pick?
What i would do is to look at the order date on the posted sales invoice and use that as the base date for calculation. And then you can deduct the value for each posted sales shipment for that invoice on the shipment dates.
Then you can put those data in a buffer table and create a report based on that buffer table if it is the not shipped order balance you want.
If it is the not invoiced balance you follow the same principal just with the posted invoice data.
