How is it possible that the Doctor remembers
every single iteration he has had in the castle?
I'm talking about this line:
The Doctor: THAT’S when I remember! Always then. Always...then. Always EXACTLY then. I can’t keep doing this, Clara! I can’t! Why is it always me? Why is it never anybody else’s turn?! Why can’t I just lose?!
[He comes face to face with the blackboard, which has the word NO! written on it; Clara stands with her back to the Doctor]
The Doctor: But I can remember, Clara. You don’t understand. I can remember it all. Every time!
(He's talking about when he sees the word "BIRD" written in the sand).
The Doctor has been dying and being reborn for over 2 billion years. Or maybe not "reborn", but a new copy arrives to do the whole thing all over again. I don't think it makes him 2 billion years old now (the last iteration, the one who didn't die, only aged like two days after the events of "Face The Raven"), but I'm confused about the "remembering" part.
Does The Doctor actually remember
every single time he has done it? Or does he just figure it out every time?