I once had a double upgrade in 2001. It was YUL-LHR. It was just after New Year and the flight was fully booked so they were looking for volunteers to take the flight the next day. I was offered 650CAD (about £350 at the time I think) and an upgrade to WT+. I happily accepted.

When I was checking in the next day they said there was a problem as WT+ was fully booked. I didn't know much about W, WT+, CW and F back then so wasn't too bothered, besides I still had the money and flight home (I was a student at the time).

They then told me I had been upgraded to CW. I thought that was a bonus but I wasn't overly excited as I didn't appreciate what it really meant. I was delighted when I go on board though.