Fascinating stuff, Listener.
In 1964 the Watchtower repoted:
As Jehovah revealed his truths by means of the first-century Christian congregation so he does today by means of the present-day Christian congregation. Through this agency he is having carried out prophesying on an intensified and unparalleled scale. All this activity is not an accident. Jehovah is the one behind all of it. The abundance of spiritual food and the amazing details of Jehovah's purposes that have been revealed to Jehovah's anointed witnesses are clear evidence that they are the ones mentioned by Jesus when he foretold a 'faithful and discreet slave' class that would be used to dispense God's progressive revelations in these last days.(Watchtower, June 15, 1964, p. 365)
In 1919, the Society teaches, Jehovah chose them as his earthly organization. Of course this begs the question of how it was made known to them. Anciently such things came through apostles who received it through revelation. If God never changes but is the same yesterday, today and forever, shouldn't the way he communicates be the same? In the quote above, we see that God would use the "faithful and discreet slave class...to dispense God's progressive revelations in these last days."
Yet elsewhere the Society stresses it does not receive revelation as the apostles did. Adding to the word of God seems to be repugnant to them, but the early Christians were strangers to the concept of a closed canon. They were not opposed to adding to the word of God, but only to adding to the words of certain books. Progressive revelations from God constituted new scripture. Yet even though the Society once went so far as to proclaim Jehovah as the Editor of the Watchtower, and the articles the messages of Jehovah to his people, it stops short of declaring the "progressive revelations" of the "last days" to be scripture.
So how can this be? Isn't it true that the GB considers itself to be a collective prophet?
Here again is what the Watchtower says:
In ancient times he sent prophets as his special messengers. While these men foretold things to come, they also served the people by telling them of God's will for them at that time, often also warning them of dangers and calamities. People today can view the creative works. They have at hand the Bible, but it is little read or understood. so, does Jehovah have a prophet to help them, to warn them of dangers and to declare things to come? ... These questions can be answered in the affirmative. Who is this prophet? ... This 'prophet' was not one man, but was a body of men and women. it was the small group of footstep followers of Jesus Christ, known at that time as international bible students. today they are known as Jehovah's Christian witnesses. (Watchtower April 1, 1972 p. 197)
I guess new light reveals the small group to be the GB.