Sagan was careful*, in working on his 1966 "translation, extension, and revision" of Shklovsky's Intelligent Life in the Universe, to typographically set his contributions apart from Shklovsky's original text.

I haven't had the free time to check if there are any fibonacci sequences or other mathematical patterns in Sagan's interpolations, but it would be most amusing if there were!

Lagniappe: https://cdn4.volusion.store/zausr-eprhq/v/vspfiles/photos/19...

* due to the Cold War, he and Shklovsky hadn't been able to meet and collaborate like normal translators and colleagues