Here's the answer to your question (since that link didn't seem very helpful):
I bought Sega Superstars for $20 with a $5 BB/McD coupon ($15 net). Then a week later it dropped to $10, so I brought my receipt and game back for the price difference....
They PM'd it to the price I actually paid, since there's no way of knowing what the terms/conditions of the coupon may have been. I got $5 back.
In most cases, they will PM to the discounted price (net price you paid).