It’s once you subscribe to an app or service (such as the rather excellent Planepoints) you realise just how often BA are swapping airframes and types.

Case in point, I’ve got a flight to Mallorca where the seating is of interest to me as we are a party of three. It’s had 5 aircraft swaps (320/321 and variants of seating plan) so far, and we are still 5 weeks out.
If you’re trying to hold exit row seating it becomes a chore.