joe,
For clarity, let's say I create a PO on July 1st for $250. I get the invoice on July 3rd for $300 ($250 + $50 shipping). I pay right away (on the 3rd), and receive the goods on the 20th. So, while your sequence has goods arrive as #3, and invoice arrive as #4 - in our business invoice arrives several weeks before goods. Similar to how we as consumer purchase online: we pay Amazon at the time of the order; not after we receive the shipment.
Therefore, I have two problems with this workflow (and that's before I get my head around allocations, which will probably never happen). Probably, I misunderstand something.
First, when I receive the invoice and make the payment. There is no correlation of the payment to the purchase order. What happens if the vendor sends another invoice on the 5th? There is nothing in the system that will hint me that I already paid for this PO.
Second, when the goods arrive there is always a reference to my PO since PO lists line items. If some items are on back order, those line items are marked as such. There may or may not be a reference to vendor invoice (more likely not). If I have 40-50 invoices that are not in the system (because the goods have not arrived yet) - how can I pick one to match the shipment? The only way is to open each invoice from that vendor (ok, from specific vendor there may be 5-10), and see which one applies to the PO that is on the shipping memo.
Is there no support for the workflow that I described? In our business 80 per cent of our purchases happen that way. And 100 per cent of our sales, including sales to businesses. There got to be some way to implement it...