With EF now blind, I'm trying to figure out true availability / upgrade probability on my ATL-AMS flight today. Upgrade list says two seats available, seat map shows two available, but if I do a dummy booking I see 'three seats available at this price'.

So where's the third seat? Secret reserve capacity? Held by a non-rev who will move to the back if the sell the seat? Does it mean they'll bump somebody if a walk-up is willing to pay full freight?