Is it alright to cover some information in the defense but not the written thesis?
n+1 methods were trialed; Method X [the one you ended up using] was the most promising [say in what sense], so it was chosen for further study.


I would not plan to cover something verbally without documenting it in your written thesis.  However, if someone asks you about something that's not in your written thesis, you may go ahead and answer to the best of your ability, even if the thesis doesn't have the answer in writing.