In The Day of the Doctor, all the Doctors came to save Gallifrey (no sir, all thirteen!). My question is: how did all the Doctors know to come? Only the three Doctors (10, 11, 8.5) were brought together by the moment, after all. So how did they know?
12th Doctor (Capaldi) knew to come because 11 (Smith) retained his own memories.
For the others it's not shown on-screen, but we can safely assume that War (Hurt), 10 (Tennant), and 11 contacted the rest of their incarnations and convinced them to come and help. Supposedly their memories of this event would also be erased just like War's and 10's, as to not pollute the timeline.