Fullmer defeated Sugar Ray for the title, then lost it back in a rematch. After the National Boxing Association striped Robinson of the title, Fullmer and Carmine Basilio fought for the vacant crown and Gene won. He finally lost the crown to Dick Tiger.
In contrast today's boxing, there was only one undisputed championship in each weight class back then.
Not exactly true. The National Boxing Assoc. was often in conflict with the New York State Athletic Commission. The state of Nevada often sided with the NYSAC. When the NBA striped Sugar Ray, he was still recognized by the NYSAC and lost that crown to Paul Pender.