I usually book domestic F on two class AA services. However on the two occasions when I've been booked in coach in the last 12 months I have been upgraded at the last minute (i.e. when already seated). There were several people listed on the upgrade list and it looked like only one person's upgrade had cleared with the tick next to the name. I was not on the upgrade list. I don't know how their system works or why I was upgraded ahead of the rest of them.