In 1968 Mansell, in London, began publication of The National Union Catalog, Pre-1956 Imprints: a Cumulative Author List Representing Library of Congress Printed Cards and Titles Reported by other American Libraries (NUC). One of the largest sets of printed volumes ever published —perhaps the physically largest— and the largest printed bibliography, it was completed in 1981 in 754 folio volumes, containing a total of over 12,000,000 entries on 528,000 pages, and occupying approximately 130 feet of shelf space. The complete set weighs 6,000 pounds. It was produced manually by photocopying library catalogue cards in LC's unique card catalogue.
Before OCLC was available outside of institutional libraries, in 1984 Breslauer & Folter, in their survey of historical bibliographical classics entitled Bibliography, its History and Development, characterized NUC as "The most extensive general bibliographical compilation of all time." In 2013, when I last revised this entry, their assertion remained valid if the scope of the comparison was limited to bibliographies printed on paper.
Around 1995 NUC was superceded in certain respects (especially ease of access, ease of updating, and shelf space) by bibliographical databases such as OCLC WorldCat on the Internet. Experts were quick to point out that bibliographical nuances and details present in some NUC entries were lost, or sometimes confused, in the electronic conversion. Whether any of those details would eventually be added or mistakes corrected in the database remained unknown.
♦ As a reflection of changing times and a shortage of shelf space, in November 2013 antiquarian bookseller Ian Jackson of Berkeley offered for sale in his Cedules from a Berkeley Bookshop, No. 28, a full set of NUC, "one of the few sets without library markings", for $754 or one dollar per volume, with the caveat that "Buyer removes." This last element was crucial as the set weighed perhaps 10 pounds per volume.
In conclusion, I cannot resist quoting Jackson's final paragraph of his description:
"Other attractions: the four volumes on the Bible remain the largest inventory in print, and in volume 671 (p. 565, s.v. Wolveridge) a presumably disgruntled employee has written 'Anyone paying good bucks for the crap in this catalogue has been royally screwed by us.' "
NOTE: When I returned to this entry in September 2020 I was surprised, but not truly amazed to learn that the entire set of 754 volumes from the University of Michigan had been digitized by Google and was available online through the Hathi Trust at this link.