Brunswick-Balke-Collender published rule books until about 1942 and were the authority. They also ran the championships and set the prizes and rules.
The game we would call eight ball did not appear in the rule book until the 1908 edition. Previous editions of the rule book ended at shuffleboard (page 116). In 1908 additional games were added including this game that BBC Co. seems to have invented to sell ball sets. They called it, with tremendous inventiveness, "BBC Co. Pool". The game continued to be called this through the 1942 edition of the major rules revision of 1925. Below is the start of that first appearance of the rules of the game.
There were many, many pocket billiard games before 1908 and thus before eight ball. The championship game in 1908 was Continuous Pool which was like 14.1 but you ran off all the balls of each rack and started each new rack with a full-rack break shot. This is the game that de Oro won pool championships at. Fifteen ball pool was scored like rotation but you did not have to shoot the balls in rotation. In Pyramid Pool the first person to make any 8 balls won. Rotation Pool, Chicago Pool, Two-ball Pool, 41 Pool, .... But no 8 ball until 1908.
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Pool games evolved over the years into what we play today for the most part, but what didn't change was that American pool was played with 2 1/4" balls back then, as well as today, although the cue balls varied in size do to the game requirements or pool table design requirements.