Hi Rich
No, I believe that field is the date the detail line on the PO was most recently edited.
The inventory master table has a field called "Last Rcpt Date". That is not quite the same as the date you placed a PO, because the PO might still be outstanding, but I think it is the closest you are going to get without having to work a lot harder.
If you are using Sundry Items instead of Inventory, you can find the "Last Rcpt Date" field there as well in the Sundry master item table.
Steve