The chairs on the Commission was ratified for a five year period every time the Commission met. If a boss died during this period, his successor wasn´t named a fully Commission member until the upcomming meeting.
Buffalo and Detroit Families seems to have been in a dissaray in the 70s. Especially Buffalo who had split into several factions, lacking leadership stability. And by the time of Bruno´s death, the Commission was solely a New York thing. The internal Philly wars created a great instability. I think I read somewhere that Scarfo was scheduled to become a Commission member in the mid 80s. But his chair was never ratified because of the turmoil the Commission case was bringing.