Well, we all know that when the Beatles actually mixed their songs (except for Rev 9 in here), they mixed to Mono.. it was George Martin who'd mix it to Stereo later with no Beatles in sight..
That's certainly true of the older stuff, but the book with the new box shows that it's not so cut and dried with the WA. Came as a surprise to me as I was previously under the impression that the stereo version came first, but it turns out that it depends on the song.