We made a shipment to a customer and they did not receive all of the parts that we confirmed and invoiced. We are filing a claim with the freight carrier for the items that are missing but we need to create a new shipping document for the parts and serial numbers that the customer actually received and track the parts and serial numbers that are essentially lost. 

I know we need to create an R order type but not sure whether we should use the RM or RR order type.
Conceptually we need a return for the parts that are lost that translates to a credit memo linked to the original invoice with the lost serial numbers and item quantity on the return shipment. Then have the RM workflow create an issue for the replacement parts that will create a new shipment and invoice when the replacement parts are shipped.
I hope this makes sense...any ideas will be appreciated.