Sampradaya or Disciplic Succession: Transparency in Disciplic Succession

                                                                  Q. Why does a particular sampradaya not just teach as it is what it believes in, instead of trying to compare and contrast with other sampradayas and constantly try to prove its view point or interpretation as the last word?

                                                                  Q. Going through a discussion on Bhagavad-Gita, we discussed regarding "Why Krishna had to start a new parampara?" During the discussion we encountered many complex understandings.
                                                                  Krishna says in beginning of Bhagavad-Gita Chapter 4, He chose Arjuna as the first one to get the knowledge of Bhagavad-Gita for the new parampara. Now our concerns are:

                                                                  Q. How can we know that the shastra is correct? The ancient traditions are oral and only recently in historical time were they written down. And we all know that when a story is told it changes from one person to the other. The new testament of the bible was written 70-100 years after Christ's death. Here your talk about thousands of years.

                                                                  Q. If Buddha and Krishna are the same Person then why is there a contradiction in Their teachings? While Buddha preached non-violence, why does Krishna justify anger and violence?

                                                                  I have seen that over time, some of the teachings of Buddha have been modified to suit the times. Could the same have happened to Krishna's teachings also?