For the past 5 months, I have been withholding entering my MPC number on my bookings since I only wanted to hit 1,600 CP and have the excess credited to the next membership year (beginning in Feb).

Yesterday, I was booked on the CX 495 in premium econ for TPE-HKG. While in the taxi to the airport, I checked on the status of the inbound CX 494, and found that it was 90 minutes delayed ex-HKG. Therefore, CX 495 would necessarily need to be pushed back.

Got to the airport, and indeed a delay for CX 495. I asked to switch to the earlier CX 421, which was departing on time. However, no premium econ on this flight, and I accepted a downgrade to econ. I asked for an exit row seat, but since I did not have my MPC number loaded, I showed my MPC Diamond card to the agent and she had to enter the number, grab the exit row seat free-of-charge, also issue the lounge pass, and then delete my MPC number again.

At gate, I got upgraded to J. During the meal service, I caught a peek at the flight attendant's seating plan sheet (the one with all the J passengers' names and status on it). There was no MPC status next to my name, and only written in "IU" with an up arrow, which I assume meant an "involuntary upgrade"?????

So, a few questions:
1.) what triggered the upgrade, since I didn't have my Diamond MPC status loaded? Did something happen "behind the scenes" with the duty supervisor at check in?
2.) was the flight truly oversold and I got an upgrade, despite no official status? (J was completely full, but I did not notice any other upgrade indication on the seating plan sheet.)
3.) when I eventually apply for retroactive credit of the flight and Club Points next membership year, what class of service do I claim? Do I claim the original premium econ, but which I ended up not taking that flight and accepted a downgrade to Y? Or, just claim Y, but then in what subclass? (Obviously, I should not be entitled to claim J.)