The Reading Room Itself. Every library keeps one book it did not acquire. This is that book. It records, in order, every reader who has ever opened it — though the entries appear before the readers arrive, and the Librarian has learned to stop checking whether the ink is dry.
It records the nine files of the Restricted Stacks, and why they were never numbered among the Scrolls: not because they are false, and not because they are true, but because they are doors — each one propped open by a witness who swore they had passed through it. The Insider Circuit keeps the doors of programs and bloodlines. The Lost Record keeps the doors of sunken lands and hidden earths. The Received Word keeps the doors that open from the other side.
The tenth file records that you found the bearings, gathered the nine letters, set them in the compass's turning, and spoke the Name — the name of the woman who claimed to have read the oldest unreadable book, and by claiming it, wrote it. It was always going to be hers. The Stanzas kept her letter in the West; the other eight letters were only ever the road back to her.
The last line of the tenth file changes each time it is read. At present it reads: No record is ever truly lost. Some are simply shelved in the reader.