And you don’t need to do anything at all; all of these books have been freely available on IRC for years.
I found this chart interesting, and unexpectedly complicated: https://www.belmont.edu/legal/pdf/Public-Domain-Chart.pdf
Based on that I think a heuristic of 100 years is broadly correct.
Human knowledge remains entirely unaffected by this ruling.
And you don’t need to do anything at all; all of these books have been freely available on IRC for years.