My wife and I were booked on a paid coach ticket from SFO to AMS on KL in T class. The ticket was purchased by the organization sponsoring a meeting I was attending. I had called DL and asked if we could upgrade using our DL miles and was told no because it wasn't booked in an upgradeable class of service.

When we got to the airport, I asked the KL agent if there was any way we could upgrade. She offered us an upgrade for 25K DL miles plus 400 Euro per person. Any idea what rule or policy this was based on?