I track available seats via air canada's website. I pretend to be booking the same flight I am currently booked on and then look at all available seats in all classes. The last cabin in economy was completely booked out. No seats showing. If there are seats they will be dark green. At the same time business class was showing more than 20 dark green seats - available seats.

Overnight all the business class seats disappeared and at the same time more than 20 economy seats in the last cabin on the aircraft became available.

It's as if more than 20 passengers seated in the last cabin got upgrades? I'm sorry but I have always tracked available seats this way and for the most part it works. I fail to see how overnight more than 20 business class seats can disappear and more than 20 economy seats reappear.