Near the end of the story, the Eleventh Doctor tells the Time Lord General that all his past selves have been working on the calculations necessary to save Gallifrey for centuries, so he is now able to put the plan into operation. But how could he have remembered this information if, once the adventure is over, all his past selves forget they experienced this, as supported by dialogue in the episode itself? Remember, it was stated that after they left, the memories of the War and Tenth Doctors would fade, so logically, the memories of the earlier Doctors would also disappear/be locked.