The board of directors was referred to as a governing body for quite a while, even though it was such only in name. After the elder arrangement was put in place in '71, it didn't make a lot of sense to have a single man as head of the organization, so the GB was enlarged and given more powers, at least on paper. They weren't happy with their lack of power, however, and there was a lot of dissatisfaction at Bethel with Knorr's autocratic rule; so after a political struggle, Knorr saw the writing on the wall and aceded to a motion of the GB taking over management of the Society.
There's a fairly detailed account in Crisis of Conscience, although it leaves out (or barely mentions) some important parts, such as a major meeting with all the Bethel elders in which complaints were aired.