I do believe that until 1969 the WTS taught that the GT had started in 1914 but was interrupted in 1918 to start up again at a later time.
*** w51 3/15 p. 164 Time Better than Money ***
When Christ was enthroned, in 1914, great tribulation was started against Satan and his wicked world organization. If it had then proceeded to completion, no flesh would have been saved. But for the sake of human flesh that tribulation was shortened or cut short, to allow a period of time for men to take in and give out knowledge of the established heavenly kingdom, before that tribulation enters its climax of Armageddon. (Matt. 24:21, 22) This time period, known as the last days of Satan’s delinquent old world, will not stretch beyond this present generation. The precious time grows short.
*** w99 5/1 p. 16 pars. 11-12 "Let the Reader Use Discernment" ***
On Thursday, July 10, 1969, at the "Peace on Earth" International Assembly in New York City, F. W. Franz, then vice president of the Watch Tower Bible and Tract Society, gave an electrifying talk. In reviewing the previous understanding of Jesus’ prophecy, Brother Franz said: "The explanation was given that the ‘great tribulation’ had begun in 1914 C.E. and that it was not allowed to run its full course then but God stopped World War I in November of 1918. From then on God was allowing an interval for the activity of his anointed remnant of elect Christians before he let the final part of the ‘great tribulation’ resume at the battle of Armageddon."
12
Then a significantly adjusted explanation was offered: "To correspond with the events of the first century, . . . the antitypical ‘great tribulation’ did not begin in 1914 C.E. Rather, what took place upon Jerusalem’s modern antitype in 1914-1918 was merely ‘a beginning of pangs of distress’ . . . The ‘great tribulation’ such as will not occur again is yet ahead, for it means the destruction of the world empire of false religion (including Christendom) followed by the ‘war of the great day of God the Almighty’ at Armageddon." This meant that the entire great tribulation was yet ahead.