About ten years ago, I found a 1954 Encyclopedia Britannica with Yearbooks from 1943 through 1979 for $20 at a Friends of the Library sale.
It is useless for learning about the latest discoveries in biotech but it is an invaluable resource for history prior to it's publication date. What other general reference will describe the Battle of Tannenberg in three full large pages with small print? The newer Encyclopedia Britannicas seem like Reader's Digest condensed books by comparison.