Jehovah’s Witnesses did Jesus choose JW's The Faithful and Discreet Slave in 1919?

I have talked to some JWs and they do not know anything about that. However, it is in their publications that they were appointed by Jesus. They were said to give the proper spiritual food at the proper time, but their teachings have changed radically since then. So, either Jesus did not appoint them or they had the right teachings then. If they had right teachings them, why to change the teachings??