On tuesday, I was at the Chennai flight, they had an quipment swap and it was a 4 class aircraft instead of a 3 class. config was 61J/32W/127Y.

There was this one guy who had a boarding card for 4A, He was orignally in 14A but must have changed it to 4A when it opened up. Anyway he gets to the gate and the gate reader pings loudly and the BA girl changed the boarding card over to a new one and said "There you go sir, i have put you back into 14A, just as you had requested in your booking"

I turned around and thought how unlucky he was. Moral of the story is that if F cabin opens up as J, they may move you out that seat so be prepared if that happens!