A couple of thoughts:
Regarding who wields the real power, it must be acknowledged that legal has much influence over the operation of the various corporations. At times, this can spill over into congregation procedure (i.e., wording of disfellowshipping/disassociation announcements, child custody issues, etc.)
Perhaps the stockholders likewise have influence and are enriched by the organization's operations. In the absence of hard evidence, this is speculative. The stockholders I have known would be wealthy without their involvement in the corporate affairs of the Society. I believe the real power lies in the power over people's lives, as opposed to power to make decisions governing corporations. The lawyers and stockholders are Jehovah's Witnesses in good standing. As such, they are under the power of the Governing Body. Without the power over people's lives, there would be no cash flow, no volunteer workforce and no need for corporations.
As far as how aware the GB is of past error is concerned, I believe Ray Franz wrote that he was unaware of certain negative aspects of the religion's history when he was on the GB. From what I know, in the post-Rutherford era, those with substantive knowledge in this area are all dead. I don't believe any on the current Governing Body are as aware of the organization's true history as are many on this board.
F.