...a book that has only been published abroad isn't really published for the purpose of US copyright law.However, the implications require more thought and work. Programs that are digitizing works that might have been published abroad will need to be more diligent in determining if the work is in the public domain. The copyright status may be muddled (my word), especially if the work had its copyright status restored.
Hirtle provides a good summary of this issue, including the implications as he sees them. He also points to additional resources on this topic.
Finally, if you are trying to digitize materials that are clearly in the public domain, you may want to use an earlier cut off date than 1923 like perhaps 1868. Using Hirtle's logic, life plus 70 means that the person died in 1939. If you assume that the person lived to be 90 and that the person published his/her work at the age of 20, then works published before 1868 would be in the public domain.
Technorati tag: Copyright