Date Requisition added to PO?

 Is there a way to positively get the date that a Requisition was added to a Purchase Order via the Autocreate process? 

The closest I can get is the date that the associated Purchase Shipment Line was created, but I've found there are times when a shipment line quantity is simply updated to accomodate the requisition quantity.  I've looked in po.po_line_locations_archive_all to see if there's data to indicate why the shipment quantity changed, but there's no mention of the requisition.

I've looked in these tables:

po.po_line_locations_all, po.po_lines_all, po.po_headers_all, po.po_requisition_lines_all, po.po_requisition_headers_all