Hi,
Do you have Source Codes in Ledger set up for IR-AD, IR-RC and IR-RT? If yes thenb, if you haven't already, you can create a Source Journal in Ledger for your retrieved from PO entries. (You can do this in pre-GL9.0A versions of Ledger also.)
Run the Source Journal report on your Ledger data for the period in question. Depending on what your PO Company Profile 'Send to GL' settings are, you will see (most likely) the individual PO document numbers in, say, the GL Reference or Description fields in the report and can use these as part of your audit trail. And, if the report is sorted or grouped by account number, you'll find the individual document entries within the accounts distributed to at that time.
Good luck!
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Regards,
Softrak Tech Support