There were always three regimes. Movie and book.

Clemenza's, Tessio's, Sonny's. Sonny did have a regime.

Later, it was Clemenza's, Neri's, and Rocco's. Neri took over for Tessio, Rocco's was a new scret regime. Sonny's old regime was split up in the existing regimes.

Then, later of course it was Pantangeli, Neri, and Rocco.