From the earliest of times of the Catholic church's Ecumenical councils were used to make major changes to its doctrinal direction. Decisions were made by Bishops, they were ratified by the Pope ... and it was done. And the laity had to accepted them or not.
And while splinter Catholic religions accepted most of these councils, non-trinitarian faiths which developed latter (of which Jehovah's Witnesses are apart) did not. Because, as to quote Wikipedia, 'They viewed the ecumenical councils ... as attempts to define dogmas (or doctrine) by debate rather than by revelation'.
This is all well and good, and I understant the scriptural argument.
However our Governing Body does not actually believe in the direct revelations from Christ Jesus or God's Holy Spirit. As mentioned many times by their public statements, that the Governing Body is 'neither inspired or infallible'.
So then, how does the Governing Body receive spiritual enlightenment, other than from simply reading the Bible, which any Christian can do?