^ auntiehill thought it up for my Christmas name. Who said anything about the Doctors steerin'? I'm talkin' abou the Tardis itself takin' the Doctors where they needed to be at that certain time.
Sorry, I was a bit ambiguous. I didn't mean to say the Doctor steered the Tardis there, rather that it would be impossible for the Tardis to be steered there, by anyone. Even itself. We know from 'Name Of The Doctor' that the Tardis had faulty navigational circuits. So the First and Second Doctors' meanderings were not (just) lack of skill at flying the thing. The Tardis, in those days, was inherently unsteerable.
I took it to be that one of the recent Doctors (likely Matt Smith) told the first Doctor to start the calculations. He likely then told each of the Doctors to come along the journey in order to make sure there were enough TARDISes to make this thing work. They all forgot because the timelines were out of sync or whatever. In fact, I'm sure the Doctor knew that would be the case. I kind of wonder if he forgot about Capaldi (but Capaldi didn't forget about him, of course, allowing him to choose to come as well to make sure it worked).