Awwwww I can picture so well the scenario and encyclopedia that you described! Their uniqueness and their value is something that makes them a object much more valuable then it's residual value... The last time that I've been in Rua do Carmo, I saw a street seller woman, that detached the pages of a old encyclopedia, and was selling page by page of the drawings and diagrams... You can picture that by selling page by page (at 10-15€) the amount of money that she will get for it! Let's hope that those pages, since they aren't going to be again reunited in the same book, became a "piece" of art only for being exposed in a wall.