New Purchase Order for a particular Customer Sales Order) - by right-clicking on the Sale in the WMS and selecting Create Purchase Order, this will open the WMS Purchase Order screen.
WMS Replicates 7 Months worth of Purchases. Once a purchase order is older than 7 months, it is marked as closed.
The OnOrder section in Item details window -> analyse -> OnOrder is the un-received WMS amount. This figure will not include orders older than 7 months.