Also notice that in the film and the novel, Tom never refers to Vito as "Pop," "Godfather" or "Don Corleone." In fact, he never uses any form of address.
Turnbull, you're a good man. But Tom does refer to Vito as Pop after they all leave his bedroom after telling him the heartbreaking news that Mike killed Sollozzo; Sonny's wants to go after that pimp Tattaglia and Tom counters with "let the smoke clear, Pop can negotiate."
