Hi
I had a return trip booked on MH which started in Oct last year and is ending this month.
I was able to see it initially on my bookings but then it vanished. When i called them at the beginning of this year, they said bookings made last year weren't available anymore due to OW alliance. So I had to choose seats over the phone.
But suprisingly, I didn't have to wait a long time over the phone and they also sent me a sms confirming my changes which was new.