In that extremity, I went into the Department of Mysteries and I invoked a password which had never been spoken in the history of the Line of Merlin Unbroken, did a thing forbidden and yet not utterly forbidden.
It’s possible that the Line reference is misleading, but if so it is an odd piece of phrasing.
The Line may not—in ch 86 Dumbledore hints he got in via phoenix travel:
It’s possible that the Line reference is misleading, but if so it is an odd piece of phrasing.