I had no luck, booked for a OW SFO/HKG for 6th Aug, in late april this year.
But I had some incidents that need me to leave on 3rd Aug.

I forgot what class the ticket was, but CX wont allow me to apply credit to rebook. I have to cancel the ticket then book a new one 1st week of July(i did in through a new agent), Once i confirmed my 3rd Aug itinerary, I cancelled the 6th and filled for refund.

Fast forward to September, Called MPC, my original agent, even a friend of mine working in International' ticket told me the the 6 Aug was still OPEN?!?! she helped me to call back to SFO office, and I have to call to CX North American Accounting to check.

Early this weekI got around 70% refund back in my AMEX, i filed an investigate.
Anyways my 3rd Aug flight was great, especially my 3 luggage got deliver quick and the new product.^