I'm new to the world of searching for upgrades, but is availability linked to your final destination? What I mean is I was just playing around with expertflyer and wanted to see if there were any flights to Europe next May that had availability to upgrade to business class. I tried London direct from DFW and couldn't find 2 available. But when I tried CDG, there was availability on the flight to London, but not on the BA flight on to Paris. Is that normal?