[U]nder the 1909 Copyright Act, when the original term was 28 years but another 28 years was possible if the copyright owners merely paid $10 and filled out a simple form. Who wouldn’t pay $10 and fill out a simple government form to get 28 years of protection? As it turned out almost everyone except for motion picture studios. Here is a sample of the renewal rates from a study the Copyright Office did:
Type of Work Renewal Percentage
Lectures, Sermons and other oral works 0.4%
Dramatic Works 11%
Works of Art 4%
Technical Drawings 0.4%
Art Prints 4%
Half of all maps, two-thirds of music, eight out of nine dramatic works and periodicals, thriteen out of fourteen books, twenty-four out of twenty-five works of art, and 199 out of 200 oral works and technical drawings are abandoned at that point.
Overall, about 78% of protected works were not renewed after 28 years, just before the regime was ended.
Current law provides much longer protection to copyrighted works, leaving the size of the public domain very small. But as the evidence above shows, the majority of all types of works but movies, and the overwhelming majortiy of many kinds of work, don't have more than negligible economic value the copyright owners after twenty-eight years.
Moreover, this listing is really more restrictive than current law which protects works that were never the subject of an initial copyright registration, works that are now also protected by copyright law.