I don't think I could have known it all along, unless the book was there in its entirety in my head before I started writing - and that seems unlikely given the way it grows as I work on it. But I suspect that my subconscious had been working away all along, making links I didn't know about and being ready to add importance to anything at all that got included, if I happened to need it later.

It's a lot cleverer than me, which is slightly disconcerting ;)