Is there a way to mark Items as Backordered on Purchase Order?

[TravelingBags]

When we place orders, suppliers often notify us that items are back-ordered or sometimes unavailable.    The issue is that when we receive part of a PO, there is no way to mark an item as Backordered, but the item is discontinued and will never arrive.  It is hard to track when we can close out a PO or to follow up and ensure we get what we ordered and paid for.  Is there a way to do this? Maybe something can be added to the PO system to better track the different statuses of items when receiving items and trying to close or monitor purchase orders.