One fact remains constant throughout the short history of this organization - whether the Bible Students or JW's - is that it's leadership has been hand picked by Jesus to represent him (and his heavenly kingdom) here on earth.
This belief (and support of this belief by the faithful) gives the leadership ultimate authority and power. To provide "proof" of their right to rule (or how they received this divine blessing) could potentially undermine their righteous and prophetically determined position.