Is it possible to received less than the shipment quantity billed?

Hello all,

Is it possible to received less than the shipment quantity billed? If so what controls the logic? I have a situation where an invoice was matched to a PO before it was received and as a result it was placed on hold (QTY REC) because quantity billed was greater than quantity received (billed = 600 and received = 0). The hold was released once the user received the PO but they received less than the billed amount. See example below:

Purchase Order                          Shipment Quantity

Number 610428                           Order: 600

Relase: blank                               Billed: 600

Line: 1                                        Received 594.50   

Ship To Chicago                          Accepted: 0 

Thanks