This is a guide to pre-1870 copyright records that never made it to the Library of Congress, many of which were generally assumed lost (even though they mostly ended up at the National Archives).
Until mid-1870, copyright registration duties were handled by the local U.S. District Court of the author or proprietor, while the work itself was deposited with the Department of State (until 1846), Library of Congress (1846-1859, 1865-1870), Smithsonian Institution (concurrently 1846-1859), and Patent Office (1859-1865, 1865-1870 concurrently). In 1870 all copyright responsibilities were centralized in the Library of Congress.
I am currently a Visiting Scholar and Professorial Lecturer in Law at The George Washington University Law School. Before this I served as the Abraham L. Kaminstein Scholar in Residence at the U.S. Copyright Office.