The novel says that, after the Great Massacre, "Now the Corleone Family was unchallengeable, and Clemenza had his own Family. Rocco Lampone was the Corleone caporegime.In Nevada, Albert Neri was in charge of security for all Corleone hotels." So, Rocco cleary was a capo. But for whom? The sentence is a bit ambiguous. Was he a capo under Michael? Or under Clemenza? If he were a capo under Michael, was he in Nevada? And why would Michael, with his "legitimate" front, need a capo in the first place.

As you know, in GFII, Rocco is little more than a rent-a-cop, while Neri clearly eclipsed him in Michael's estimation. Not surprising: Rocco was Clemenza's recruit, Neri was Michael's. Small wonder Michael asked Rocco to make the ultimate sacrifice at the Miami airport--he was expendible.