This post explains the calculation within the Purchase Orders field in the Inventory Part Currently On Hold window.
Purchase Orders = Part Received + Parts to be received
For the calculation POs with Order Code 6 is not considered and the quantities in the Purchase Order Lines (POL) are considered.
Part Received (Purchase Order Line status != Released)
Part Received = (Due at Dock - Scrapped Qty at Supplier) * Inv Conv Factor
Parts to be Received (Purchase Order Line status = Released)
Parts to be Received = Quantity * Inv Conv Factor
Note: Even if the Purchase Order is in Status = Planned, the quantities are considered as the POL is in Status = Released.