Lost works is a huge problem in movies and video. Film does not store well. I remember reading an article back when they released restored DVD's of "The Might and the Mighty" and "Island in the Sky" of how difficult it was to find copies of the original in usable condition and how long it took to actually restored the damaged originals. I bought the restored DVD's back in 2005 when they came out.
http://articles.sun-sentinel.com/200...hn-wayne-films
Not everyone has the money and desire that John Wayne's family did.
In theory, every book that went under copyright since 1870 is in the Library of Congress. That was a requirement of copyright according to the Copyright act of 1870. I suspect that was superseded when the requirement to register was dropped.
This, is of course, one of the great flaws of copyright law. Copyright holders love to talk about property rights without ever acknowledging any obligation to the public.