Carl Sagan never actually said "Billions and billions" until his last book. Sagan does carefully define
billions for his audience, and frequently says the word alone.
The phrase was made popular by Johnny Carson, and was grabbed by other comedians, even unto Berke Breathed. In the book, Sagan does "say" the phrase just to make us all happy.
Sagan will not be the only person remembered by history for a catchphrase he never actually said.