This paper has demonstrated that it is almost impossible to determine with certainty whether a work published from 1923 through 1963 in the US is in the public domain because of copyright restoration of foreign works. First you have to determine if the work was also published abroad or if it is based on or derived from a work published abroad. If a foreign edition is found, one then has to establish the order of publication, and whether the foreign publication occurred less than 30 days before the US publication. If foreign publication was more than 30 days before American publication, one next needs to determine if publication occurred in an eligible country and if at least one of the authors of the work was living in or a citizen of an eligible nation. Checking the copyright renewal database is still important, but only after one has determined that the work’s foreign copyright was not restored or that it does not draw upon subsisting foreign copyrights.
Copyright restoration has been criticized for unnecessarily removing thousands of foreign-published works from the public domain in the United States. What has been little noticed up to now is its negative impact on the determination of the potential public domain status of works published in the US. In many cases the impossibility of determining with certainty the absence of subsisting foreign copyrights in American publications that otherwise would be in the public domain means that American institutions will either have to keep these works inaccessible to the general public or risk the possibility of an infringement suit.
Peter Hirtle: Copyright Renewal, Copyright Restoration, and the Difficulty of Determining Copyright Status, D-Lib Magazine Volume 14 Number 7/8, 2008