Do Mormon prophets contradict each other?

Joseph F Smith taught that God is ever increasing in knowledge, Bruce McKonkie said absolutly wrong, Brigham young taught that Adam was our Heavenly Father and father of Jesus at the endowment ceremony in the temple, church saya misunderstanding of his words, Pres Hinkley told Larry King that the saying,"as man is God once was and as God is man may become, Pres. Hinkley said he wasn't sure about it, just a couplet, isn't taught much. Brigham young said Black men would never have exaltation, church gives them rights to exaltation. Brigham Young taught poyligamy necessary for exaltation, Hinkley said it was false doctrine to Larry King. What's going on?