You aren't full of it, Tim (at least not this time
). The Invoice number is stored in the PO Line item record in the receiver file. One way to see it (other than Maintain Database) is to go into AP-C as if you are going to enter an invoice for the PO, and when it says there is nothing to invoice, choose View All to see the lines anyway.
There is also an add-on (AP-T) inquiry program that will show that information but I think you have to start with the Invoice or Check number and work backwards, not with the PO number.
And as soon (later tonight or tomorrow, I hope) as I get the update posted with the Drill Downs you saw in Phoenix, you can set up your own grid and display it yourself.