Well, Kurtz clearly said that before Lawrence Kasdan was even brought on, after Lucas had made changes himself. Remember that Lucas isn't given a screenwriting credit for ESB - Brackett and Kasdan are.
Therefore, it seems likely that once Kasdan was brought on board, the screenplay was altered significantly from Brackett's original draft.
Speaking of which, I have Brackett's script, and still haven't given it a read. Maybe I'll do that tomorrow.