We always book 5EF because we prefer them. However when I went to print our boarding passes for BA207 on Monday at T-24, 1A and 1K were available if I had wanted them. So you may be lucky, if you go to MMB at T-24.

As posted on another thread we may be surprised at the number of people who don't choose their seats in advance.

On the actual flight there were 9 out of the 14 seats actually occupied, including 1A and 1K.