I know that this has been discussed previously about the 607 B.C.E and the 586 B.C.E. debate. But I found it interesting in the October 1, 1926 WT the quotes under the subheading:
"The Prophetic Seven Times of the Gentiles"
"As has already been acknowledged by many Bible students, the lease of Gentile power, commencing in Nebuchadnezzars's first year, 606 B.C.,reaches unto approximately 1914 A.D., at which time the lease was due to run out.* But as it was about 19 years after the commencement of the universal kingdom by Nebuchadnezzar before the complete downfall of the Jewish kingdom and before the crown was removed from Judah's last king, so it has been found interesting as well as logical to calculate the "seven times" of 2520 years from 588 B.C. when the Jews were completly subjugated and this brings us to approximately 1934 A.D.
"Thus from all the facts we are able to gather it would seem that the times of the Gentiles in the last and final sense are due to run their full course by the last date named above, when there might be reasonably expected, events and developments of the very great moment in evidence. We are making no predictions, nor hastily arriving at any visionary or fanatical conclusions. We are patiently biding the time and waiting for the days to disclose what may be the program of events. The most we are doing is exercising our privilege of soberly looking at the facts of prophecy and history in the light of present day developments, and therby recognizing that there is a remarkable synchronizing of circumstances and events in these days with the prophetic times."