How old does an original song have to be to be eligible for public domain?

Works published with notice of copyright or registered in unpublished form on or after January 1, 1923, and prior to January 1, 1964, had to be renewed during the 28th year of their first term of copyright to maintain copyright for a full 95-year term.

With the exception of maps, music, and movies, the vast majority of works published in the United States before 1964 were never renewed for a second copyright term.

from 1922 or earlier and/or 70 years after the authors death

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