FWIW, I am in the middle of a trip I had originally booked to CUN last June. As fares dropped and the triple MQM promotion was announced I cancelled my original K fare of $616.00 and rebooked and PAID for a new $468 flight with a K fare. The agent was able to transfer my PMU to my now new trip. Of course with the flu in Mexico we ended up in Jamaica, I was able to use 2 $400 vouchers to pay up to a F and I class itin.

The original agent was very specific about my not being able to use my leftover credit in booking the CUN trip for which I would have received 2x mqm's. As i was in the process of booking a LAS trip for next week at that time she said I could book it using the remaining credit from the CUN trip and still get my 2x mqm's on that trip.