I stand corrected. That said, at the time of Grant's writing copyright in the US was 28 years (with an optional extension for another 14 if the author lived lo

I stand corrected. That said, at the time of Grant's writing copyright in the US was 28 years (with an optional extension for another 14 if the author lived long enough), which means that OP's proposal of 25 years would likely have been sufficient to motivate Grant.