Supplier Amount Vouchered Amount (AYPD) does not include credits

We enter a voucher and then offset a prepayment when we send funds to vendors prior to receiving the goods.  When the actual goods come in - we then voucher against the purchase order to clear it.  When we run the R04802A it does update the amounts.  It seems to count both vouchers but not the payment offset we have in AP.  Is there a way to include all? or would we need a different process to prepay vendors prior to receiving goods?