Is there a way to get SAP to show the invoice reference i.o. the SAP document number? That would make it so much easier to track back older bookings. Apart from that you're forced to look up every invoice related to that SAP document, which you won't have too with the actual invoice reference, it also costs an extra session to do so. There is a tab that says reference in the last tab of the po history, but that is always empty.
It's a very time consuming process and with the limited amount of sessions, also very frustrating, as it prevents you from being able to check and compare more then 3 invoices.