It was fine the way it was. I didn't want my AP clerk to be able to modify a bill after they created the bill but I did want them to be able to create a vendor credit memo and apply that credit memo to an open invoice.

Similarly, with AR.  Because this "update by the brains at QBs" affects both AP & AR in applying credits (prepayments in AR).  By giving an AR clerk the ability modify an invoice actually fixes the ability to apply credits in both AR & AP.

It worked fine forever - why make any change at all?