Quickbooks Enterprise Contractor reports not showing PO#'s

I'm using Quickbooks Enterprise Canada, Contractor desktop edition and am trying to produce a report that shows me the PO# that a vendor's invoices have been assigned to.  If I run a Transaction List by Vendor or a Vendor QuickReport and customize it to add P.O.#, nothing shows in that column even though 90% of his invoices have been assigned to a PO.  In fact I can't find any report that shows anything in the the PO# column.  What I really want to do is check all contractors invoices to make sure they've been assigned to a PO (since someone else was entering before I took over) so I can close an old PO and be confident all it's costs have been captured.