In 1909 the US switched from a term of 28 years extensible by 14 if the author lived, to a term of 28 years extensible by 28 if the author lived. It didn't grow to life +50 until 1976.
Edit: I think the confusion may arise from the Berne convention. The US did sign, but not until 1988.
Edit: I think the confusion may arise from the Berne convention. The US did sign, but not until 1988.