They use Matt 24:45-47 simply because it gives them some authority over the people and teachings..
It does not require arguing over 1914 or 1919.
They used 1919 because that is when the conventions began to where they started the preaching to illustrate that they were not bound by Babylon.
The only reason that the FDS is of relevance to you all and them is because Jesus made a reference to it. People have this belief that if Jesus says so, then we have to listen.
From 1879 to 1974 the governing body was they board of directors. Then it was expanded and made separate, then made more separate in 2000. How the FDS was defined did not change where the teachings came from or authority. It just was done to appease people.