Current US law extends copyright protection for 70 years after the date of the author’s death. (Corporate “works-for-hire” are copyrighted for 95 years after publication.) But prior to the 1976 Copyright Act (which became effective in 1978), the maximum copyright term was 56 years (an initial term of 28 years, renewable for another 28 years). Under those laws, works published in 1955 would be passing into the public domain on January 1, 2012.
“What Could Have Entered the Public Domain on January 1, 2012?,” Center for the Study of the Public Domain