If they considered this merely a hiding problem then to never ever have considered whether it might be possible to hide from them after all, or to not have considered a legendary item of hiding in that context would be pretty incompetent.
My impression was that it was legendary in the sense of "yeah, we tell those stories to our children" instead of "look, every student's sat under the Sorting Hat, it exists and there are thousands of witnesses." That's an unfortunate part of magical stories- it's hard to avoid the Every Rumor Is Completely Correct trope without inundating the reader with worthless information, and so when you say something is legendary it's not clear whether you mean it's +6 or it probably doesn't exist.
- This thread has run its course. You will find newer threads in the discussion section.
Another discussion thread - the fourth - has reached the (arbitrary?) 500 comments threshold, so it's time for a new thread for Eliezer Yudkowsky's widely-praised Harry Potter fanfic.
Most of the paratext and fan-made resources are listed on Mr. LessWrong's author page. There is also AdeleneDawner's collection of most of the previously-published Author's Notes.
Older threads: one, two, three, four. By tag.
Newer threads are in the Discussion section, starting from Part 6.
Spoiler policy as suggested by Unnamed and approved by Eliezer, me, and at least three other upmodders:
It would also be quite sensible and welcome to continue the practice of declaring at the top of your post which chapters you are about to discuss, especially for newly-published ones, so that people who haven't yet seen them can stop reading in time.