As a PO is submitted by a buyer to a supplier, the PO is shown to the supplier for confirmation.
Each order line is sent with status "unconfirmed", as supplier is expected to confirm each line of the purchase order. As the delivery process progresses, supplier can update the delivery status of each PO line. Buyer see the delivery status update in real time, as opens the PO.
The subsequent delivery statuses of the PO are shown in the attached slide: