He said "At first, I was a button." I inferred that, by II, he must have been Frankie's consigliere or maybe a caporegime, considering how close he stayed with Frankie.
Good point. Going by the Family Org Chart from the Lebo book, Willie is listed with "Buttons - Soldiers". Maybe there are different ranks of Button like Button First Class, Second Class, etc.
:), but after that Chart, with Frankie promoted, did Willie move up the to Capo spot or did Carmine "The Plunge" Coronda leap-frog Willie?