Authority is automatically conferred to the winning aspirants to the F&DSlave title based on their works, message.
The Watchtower message, a winner: the central doctrine from 1918-1925 was: " The world has ended, Millions now living will never die" . a winner.
The world ended invisibly in 1914, as "Jesus" started ruling invisibly again.
Such winsome doctrines automatically confer teaching rights to the wtbts.