Yikes. Hard to keep that logic straight.................
What version of MAS? One might think the long term way to track this data (v4.4 and later) would be with a UDF pulling the data from the invoice entry fields (if you posted the invoice at time of ROG). But then again, theoretically, you should be able to use the PO value once the invoice is posted as the PO value changes to the invoice value (another dear old WAD). This falls apart if you have multiple receipts with multiple invoice values. Only the last one is kept in the PO file.