As a concept it existed in one way or the other pretty much ever since the printing press.
The original treaty, if I am not misunderstanding here: https://www.wipo.int/en/web/treaties/ip/berne/summary_berne includes a "dead + 50 recomended" protection since the 1908 revision, before that it was up to each country laws, and in 1948 it changed to "dead + 50 minimum mandatory". In 1993 it was raised to "dead + 70" in the UE, to be followed by the US with the same extension in 1988 in Sonny Bono Act https://en.wikipedia.org/wiki/Copyright_Term_Extension_Act.
You're not contradicting anything I'm saying, you're just saying the same thing with more words because you don't understand where my argument comes from. What I don't understand is why you would even want to take credit for such a broken system to begin with.