If you find a way to get them to honor the fare classes that were booked, please let me know. I am in a similar situation. Someone posted that Delta twitter said that underlying base fares do not matter on the international legs. If someone could find that in documentation, this argument would be solved. What irritates me, is the difference in MQDs/MQMs could potentially impact me in the future. Luckily, this year, I qualified for Diamond in mid-April, otherwise I would search until I found language that overruled what Delta is saying.