This statement is fairly inaccurate. If you check Peter Madderom 1966 thesis, you'll see that it states the earliest work on automatic differentiation was done

This statement is fairly inaccurate. If you check Peter Madderom 1966 thesis, you'll see that it states the earliest work on automatic differentiation was done in the 1950s. It's just that back then, it was called Analyitc differentiation. You can see many of the key ideas already existed back then, including research into specializations for efficiently applying the chain rule. https://academic.oup.com/comjnl/article/7/4/290/354207 https://academic.oup.com/comjnl/article/7/4/290/354207