How has the length of copyright protection expanded over time?
1790 28 years (14 years from publication; and one more 14 year extension, if the author is isn’t pushing daisies).
1831 42 years (28 years from publication, and one 14 year renewal option).
1909 56 years (28 years from publication, and renewable for up to 28 years).
1976 Life of author, plus 50 years; 75 years from publication, or 100 years from creation.
1998 Life of author, plus 70 years; in the case of anonymous works, protection extends 95 years from publication, or 100 years from creation.
