"For everything published in 1950 the original copyright length was 28 years, but it was retroactively extended with the 1976 copyright act."
Not necessarily. Works published prior to 1964 have fallen into the public domain in the United States unless the owner explicitly filed a copyright renewal.
Anything published in 1964 or afterward did get automatic renewal and extension to the new 95 year period under the 1992 Copyright Act, so the magazines after 1964 are definitely questionable.
The Stanford library has a database that lets you look up the copyright status of post-1923 (before that is definitely public domain), pre-1964 works.
Not necessarily. Works published prior to 1964 have fallen into the public domain in the United States unless the owner explicitly filed a copyright renewal.
Anything published in 1964 or afterward did get automatic renewal and extension to the new 95 year period under the 1992 Copyright Act, so the magazines after 1964 are definitely questionable.
The Stanford library has a database that lets you look up the copyright status of post-1923 (before that is definitely public domain), pre-1964 works.
https://collections.stanford.edu/copyrightrenewals