IDoc, Posting Payments, and Payment Advice

We are receiving payment advices, some referencing the invoice, some referencing the packing slip #.

Our issue is that the ones that come through with the packing slip #, when you post the payment, it does not recognize the line items that reference the packing slip number.

Is there a way to make the posting recognize both the invoice # and the packing slip # for the payment advice?

Thanks!