Although one or two nine ball events took place before it, I think the WPBA must be viewed as having adopted nine ball as its competitive discipline when the WPBA Nationals became a nine ball event. I think that was in either 1980 or 1981, more likely 1981.
The WPBA was formed in 1976, and Jean Balukas competed in its earliest events as a late teenager. Jean was in her early twenties when the WPBA switched to nine ball.