"So the slave was appointed in 1919...then it wasn't...then it was."
No, that's not what the publications are saying. Londo111 mentioned this in his first post on this thread. The 2013 Watchtower says that the appointment of the slave over all the master's belongings did not occur in 1919; the article does not say that the slave wasn't appointed in 1919. The God's Kingdom Rules book is referring to the org's current teaching that the slave was appointed (in general) in 1919; that does not conflict with the Watchtower article, which says the slave was not appointed over all the master's belongings in 1919.
So, to summarize, the org says that a small group of anointed men was appointed as the faithful and discreet in 1919, but that this slave wasn't appointed over all the master's belongings at that time; it will be appointed over all the master's belongings in the future - during the great tribulation. In other words the slave was appointed in 1919, but will be given a greater appointment or enlarged responsibility ("over all the master's belongings") during the future great tribulation.