http://www.jwfacts.com/watchtower/1919-derived.php
This far out from bothering with their silly stuff, my head spins when I try to make sense of the general doctrine. From jwfacts, I sort of remember that 3.5 years (from Rev. 11:2,3) would pass from some point in 1914 where the temple was trampled for "42 months" and that meant that Christendom was sure it had defeated Watchtower. They fudge that 42 months to end it in June of 1918 when the Watchtower Board of Directors were arrested. But some time after this 42 months (apparently 9 months with no explanation of why it was that time period), Watchtower's Board of Directors was released from prison and that release indicates that Jesus chose these men as his faithful and discreet slave.
Regardless of how anyone tries to understand this, it is a play on 1914. They chose that year for Jesus invisible arrival (after changing it from 1874) and the things that Rutherford did some short years later had to be made to fit with their predictions. Rather than admit they were wrong, they piled on to their doctrine with even more specific details of how actual events were prophesied in Revelation.
Since there is so much fudging in that explanation, they apparently returned to it in 2013 and "simplified" it and seemed to ignore the fudging to simply say that, instead of 1918, Jesus started inspecting "and cleansing" the temple in 1914 to get us to 1919- HOW? I DON'T KNOW!
I think they actually expect people not to do the math so that they don't realize that starting at any point in 1914 and adding 3.5 years will never get you to any point in 1919. They were probably wrong and got letters pointing that out, so in the Nov. 15, 2014 WT, they added the 3.5 days (again, totally ambiguous length) back to the chart with the 3.5 years in order to arrive in 1919. Here's that explanation:
"How long did this inspection and cleansing take place. It extended from 1914 to the early part of 1919. This period of time includes both the 1,260 days (42 months) and the symbolic three and a half days referred to in Revelation chapter 11."Watchtower 2014 Nov 15 p.30
Trying to understand deeper than that is just a waste of my time. I will guess that all the specifics about the slave being arrested and vindicated was too much for people to remember and sounded weird, so they came out with a simple explanation that actually made no sense. Here's my paraphrase: Y'all know Jesus came in 1914 and chose the Watchtower as his spokespeople. Well, even though they were his chosen people, Jesus had to clean it up for a few years and then he appointed the Slave in 1919. Our doctrine is so steeped in these dates that we can't abandon them, so just learn to accept them.