I was under the impression that Millionaire and Kill for a Dream were the two Andy-penned DGSS songs that were submitted during the DOYS sessions but Noel chose Nature of Reality instead.

I remember Andy saying he submitted 3 songs. Noel definitely said Millionaire was one. And I remember a DGSS era interview when asked if the "Life's too short not to forgive..." lyrics from "Kill for a Dream" were inspired by the Oasis breakup, Liam (I think) said it was actually written while Oasis was still together. (Though it could've been during the last tour I suppose...)

Also, Noel mentioned in several interviews that he was already familiar with several DGSS songs cause they had been considered for Oasis albums - he definitely mentioned The Roller, Millionaire and The Morning Son but I really don't think he ever said Four Letter Word.

Anyway, unless some evidence can be submitted otherwise, I'd say the safest bet is to guess that Four Letter Word wasn't around until DGSS was gearing up.

Did Andy not say that it was about the breakdown of his first marriage? I'm pretty sure I read that somewhere.

You can't have 11 same sounding songs on an album.

You could always try and ask him via Twitter!