yadda
All the "proof" is in the interpretation of the events by the Watchtower. JWs did not see Christ. They did not see Satan. There was no visible evidence that Jehovah selected the Watchtower. (In fact, the organization was pretty much in disarray at the time in 1919.) Since Russell had predicted that the Bible students would be raptured in 1914 or thereabout, many were disappointed when nothing happened. So a few of the diehard faithful relied on Rutherford and his interpretation of scripture to explain away Russell's failures. The shifting of the date from 1874 to 1914 was one way. And the identification of 1914 as the beginning of the time of the end instead of its end was another.
It reminds me of what happened to the Adventist movement after Miller's failure. Some said that Christ had come to the heavenly sanctuary (invisibly) and was "tarrying" until he came on the clouds to render judgment. It was a convenient interpretation that could not be proven. SDA church still holds to this explanation, I believe.
It will be interesting to see how the Watchtower will deal with the 1914 date as we approach the 100 year anniversary in 2014.