There is some evidence that Rutherford first mentioned 1914 as the beginning of christs second coming in the 1930`s.
As shown in my quote from the 1929 book Prophesy (above) he knew about 1914 in the 20's at the latest. I'm sure there are earlier quotes.
Page 133 mentions this again along with a footnote explaining that a clearer understanding of Biblical chronology pointing to 1914 was published in 1943.
The change here was nothing to do with 1914. It was down to fact that they thought the destruction of Jerusalem was 606 BCE and 2520 years gave them 1914 CE. When someone pointed out their arithmetical error they changed 606 to 607. They had the answer they wanted (1914) already. This was the change in "The Truth Shall Make You Free". The previous year (1942) the publication New World had stated 606 BCE. Page 77.
George