An arrangement has been reached with the Libraries, and the Keeper records its terms carefully, as one should with Librarians.
You may now bring your surplus blueprint volumes to any Library and trade them toward the one blueprint you actually want. The terms are theirs, not ours:
They take payment up front. The volumes you offer leave your possession the moment the bargain is struck. What you asked for is delivered on your next visit to a Library. They are in no hurry. They have never been in a hurry.
One open bargain at a time. The Librarians do not run accounts.
And a detail worth knowing: how much they are willing to trade grows with your crafting mastery in that discipline. Practiced hands are extended more credit. The Libraries know whose work is worth their while — do not ask how.
If you regret a bargain before it is fulfilled, you may withdraw it — and the volumes you paid are returned to you, every one. The Librarians keep nothing taken unwillingly. What they keep, they keep with consent. It matters to them.