RChavez, thanks so much - that seems to be the mystery solved! How long does it take for them to finalise equipment changes? I booked the tickets last Saturday, and the AAgent wasn't able to assign me seats then, almost five days ago. I'd quite like to get the best possible seats assigned sooner rather than later, as most of the planes from Miami tend to be MRTC-less and I haven't travelled economy for a while! BA's WT+ is a saviour, albeit a pricey one.