Here's the official Copyright laws in the United States, last time I checked.
Unpublished works
Death of the author + 70 years
Works from authors who died before 1939
Unpublished anonymous and pseudonymous works, and works made for hire (corporate authorship)
120 years from date of creation
Works created before 1889
Unpublished works when the death date of the author is not known
120 years from date of creation
Works created before 1889
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Published Before 1923
In Public Domain
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http://www.copyright.cornell.edu/res...blicdomain.cfm