Where was it stated that the Potter family's noble status is a result of baby-Harry killing Voldemort?
Chapter 86
"That was how your House came to be ennobled, Mr. Potter," injected the solemn voice of Professor McGonagall. "There is an ancient law that if anyone ends a Most Ancient House, whoever avenges that blood will be made Noble. To be sure, the House of Potter was already older than some lines called Ancient. But yours was titled a Noble House of Britain after the end of the war, in recognition that you had avenged the Most Ancient House of Monroe."
This is a new thread to discuss Eliezer Yudkowsky’s Harry Potter and the Methods of Rationality and anything related to it. This thread is intended for discussing chapter 114, and also, as a special case due to the exceptionally close posting times, chapter 115.
There is a site dedicated to the story at hpmor.com, which is now the place to go to find the authors notes and all sorts of other goodies. AdeleneDawner has kept an archive of Author’s Notes. (This goes up to the notes for chapter 76, and is now not updating. The authors notes from chapter 77 onwards are on hpmor.com.)