P4312 Option 9 with Receipt routing

Our understanding of option 9 in P4312 is that once an PO line is in receipt route, the PO line can not be cancelled until the quantity is updated to in-stock through the receipt route.  We receive EDI 856 / 861 transactions to move the PO into receipt routing.  In some cases, the quantity entering into receipt route will be different than the order quantity.   For example, we ordered 500 and 300 went into receipt route.  This left 200 in the Open quantity on the PO line.  We wish to cancel off the 200 but the option 9 in P4312