In fact, the phrase "governing body" never occurs in the bible ever
Their justification for the use of the term “governing body” is based on Hebrews 13:17, “Be obedient to those taking the lead over you…”
In the original Greek, the phrase “those taking the lead over you” can also be translated “the ones governing you”.
Since the concept of a “governor” appears there, they run with it and hinge on it what is their sole unchangeable primary doctrine, which is this:
”The governing body speaks for God. What they say should be treated literally as if it came from the voice of Jehovah himself”.
Beyond that, anything - literally 100% anything - is subject to the “new light” treatment. But the “obey the governors of you” concept will never ever ever EVER change.