[posted to commons-l and wikien-l; someone may want to forward it to wikisource-l, perhaps?]

I've just run across this article, which might be of use in helping those who work on the eternal problem of determining whether or not a given 20th-century work is in copyright in the US.

http://www.dlib.org/dlib/july08/hirtle/07hirtle.html

Copyright Renewal, Copyright Restoration, and the Difficulty of Determining Copyright Status - Peter B. Hirtle, Cornell University

D-Lib Magazine, July/August 2008 Volume 14 Number 7/8

"It has long been assumed that most of the works published from 1923 to 1964 in the US are currently in the public domain. Both non-profit and commercial digital libraries have dreamed of making this material available. Most programs have recognized as well that the restoration of US copyright in foreign works in 1996 has made it impossible for them to offer to the public the full text of most foreign works. What has been overlooked up to now is the difficulty that copyright restoration has created for anyone trying to determine if a work published in the United States is still protected by copyright. This paper discusses the impact that copyright restoration of foreign works has had on US copyright status investigations, and offers some new steps that users must follow in order to investigate the copyright status in the US of any work. It argues that copyright restoration has made it almost impossible to determine with certainty whether a book published in the United States after 1922 and before 1964 is in the public domain. Digital libraries that wish to offer books from this period do so at some risk."

The minefield is even murkier than we thought, it seems.