my thought on this was doing a saved search and looking at the most recent item fulfillments tied to the same sales order and pulling those document numbers onto the most recently created invoice with a script

we have a process that invoices item fulfillments and relates the two with a bidirectional link (IF => Invoice, Invoice => IF). but that’s an entirely custom process. otherwise, there is not necessarily a connection between the two, though you may be able to trace somewhat via query.