One outstanding quote where it is claimed Jesus approved the org in 1919 is 'God's Kingdom of a Thousand Years Has Approached' (1973), p. 352-3 "The 'Slave' That Lived to See the 'Sign'":
Similarly, in the year 1919, Jehovah did "turn [his] hand back upon those who are insignificant." (Zechariah 13:7) Jehovah’s Shepherd-King, Jesus Christ, did begin regathering the scattered "sheep." Like the slave’s master in the illustration, the Lord Jesus did return to his house and inspect the situation within it. He did find there a "faithful and discreet slave" class that was striving, in spite of world conditions, to do as commanded, give the Lord’s "domestics" at the proper time their spiritual food, food taken from the inspired Word of God. So the Lord showed his favor by regathering them into a well-organized body of "domestics" in his house. The eight-day general convention held at Cedar Point, Ohio, on September 1-8, 1919, was a notification to all the world that the invisibly present Lord Jesus Christ was regathering his faithful "sheep." It indicated to the world who it was that the returned Lord Jesus had found to be his "faithful and discreet slave" class. This made the "slave" class happy. It meant their being retained in the service of their heavenly Master.