might I also add that trying to change a flight upgraded using AM is a pain in the neck

CX considers that your have used a designated amount of AM to purchase an 'upgrade coupon', which (same as a redemption ticket) requires US$50 to change or US$120 to cancel. That is of course on top of your original ticket's change fee & fare difference

From experience this year, to change an upgraded flight (date &/or port(s)) you'll need to;
1) book your desired new flights;
2) check that availability exists
3) call CX to apply your 'upgrade coupon" to your new flight;
4) pay the change fee; &
5) cancel the old booking (ifyou no longer want it)

So personally I wouldn't recommend upgrading in advance using AM to any traveller requiring flexibility or on a highly uncertain schedule...