In Christian hymnbooks today it is common to find hymns that were written in the 1700s or 1800s. However, most of the time these hymns have been adapted, to modernize older language, or to adjust the meaning of a phrase for a broader audience.
According to current copyright law in the United States, printed works published before 1923 are in the public domain. Are the adapted versions of pre-1923 hymns that appear in current hymnbooks also in the public domain? What about translations?
An example is the hymn "How Firm a Foundation." Different texts can be compared here: https://hymnary.org/text/how_firm_a_foundation_ye_saints_of/compare
I am interested mainly in the United States copyright / public domain law.