(1) …one of my ongoing annoyances in life is people thinking they can rewrite Paul's lyrics to make them more "logical."
(2) I've always taken the radical position that Paul knew exactly what he was doing.
(3) Great art is rarely neat or logical.
(4) In the case of "Yesterday came suddenly," he's expanding the song's timeline to look beyond the immediate disappointment he's experiencing now.
(1) I’m not trying to rewrite the song. I’m showing strong internal evidence that an error has crept in, and that Paul’s original intention was “yes, today came suddenly”.
(2) Like any human, Paul can make mistakes, and many of his mistakes are on record.
(3) (“Great”?) art may not always have to be neat and logical, but sometimes (whether “rarely” or not) it must be logical in order to achieve the artist’s intention.
(4) The song’s timeline is a period of less than 48 hours. “Suddenly I’m not half the man I used to be” is in the present tense – being uttered “today”. So “yesterday came suddenly” cannot be made to fit using any fanciful rationalization.