I can't remember off the top of my head whether one would expect to be able to detect a Titan aircraft from an EF seat map. If you can, then it would seem to be worth checking all of the LGW-AMS flights and all of the AMS-LGW flights that day (together with the aircraft type listed in the EF flight availability information), plus the late flights the previous day, to try to see exactly what the plan is for the Titan aircraft and for all of the BA aircraft operating the remaining flights.

I wonder whether one possibility might simply be that the first AMS-LGW and the second LGW-AMS flights have not yet been swapped to Titan even though BA's plan will ultimately involve Titan operating those as well.