Eliezer (about Sublimation):

"Ramarren, Banks added on that part later, and it renders a lot of the earlier books nonsensical - why didn't the Culture or the Idarans increase their intelligence to win their war, if it was that easy? I refuse to regard Excession as canon; it never happened."

Just a technical (or fandom?) note:

Sublimed civilization is the central plot of Consider Phlebas (Schar's world, where Mind escapes, is "protected" by sublimed civilization - that is why direct military action by either Iridans or Culture is impossible).