Single vendor invoice for multiple packinglsips

Our client AR team did not invoice a vendor from 2012 and now they have more than 10000 packslip lines to invoice. All transactions are for same vendor and have multiple Purchase orders.We would like to post one invoice for 2012 & one for 2013.
The catch here is they have posted settlements using GL journal. In this case how to check relevant ledger account balance and adjust??
Client is using AX V4 , Need some suggestions to handle this case.

Wondering on how the settlement came into the picture without having the Invoices posted for the Orders. Could you please clarify what do you mean by below statement.