Well TB, given the context, Rocco was Clemenza's Capo. Remember, Michael tells Frankie that his family is still called Corleone. So, Rocco is the capo for the Corleone family under Clemenza in NY.
Michael said that in the film. The novel says Clemenza had his "own family." But then again, Frankie thought of it as his own family.
By the way, think of all the money the Corleones saved by their stingy designation of capos.
...to say nothing of Xmas gifts. If Kay had been buying Xmas gifts for the post-Great Massacre Corleone Family, her shopping trip would have ended earlier...
