sinis said: "After all, is this not how the WTS originally came up with the year 1914????"
No.
http://www.jehovahs-witness.net/watchtower/bible/203740/1/Pyramidologists-the-Great-Pyramid-of-Gizeh
From the inception of Jehovah's Organization, the proclamation of Christ's Millennial Reign beginning in 1914 CE has always been taught to begin after the Gentiles Times as foretold in God's Word. The 2,520 years from 607 BCE.
Thy Kingdom Come 1898 Edition
And the parallelism continues to the full end of the harvest of this dispensation-until the overthrow of the professedly Christian kingdoms, really "kingdoms of this world," and the full establishment of the Kingdom of God in the earth at A.D. 1914, the terminus of the Times of the Gentiles. (See Vol. II., chap. iv.) Page 126, Thy Kingdom Come 1898 Edition
They attempted to corroborate Biblical time periods with the Great Pyramid for two reasons:
1. What was stated in Isaiah 19:19.
In that day there will prove to be an altar to Jehovah in the midst of the land of Egypt, and a pillar to Jehovah beside its boundary. Isaiah 19:19
2. Who built the Great Pyramid?
One of the enigmas about the Great Pyramid is who built it. It's been stated that the design, construction and astronomical calculations found on the Great Pyramid determine that it was virtually impossible for the Egyptians to have designed it. Simply put, the knowledge displayed in the Great Pyramid was too advanced for humans of that time.
The attempts to corroborate Biblical time periods with the Great Pyramid are summarized as follows:
The Corroborative Testimony of God's Stone Witness and Prophet
For simplicity we will take our erroneous A.D. as the standard, and will scale down the Pyramid figures to correspond, by deducting one and one-fourth inches from them, so that they will correspond with our common reckoning. Thus reduced, they would show (a) 1875 less 1 1/4 equal 1873 3/4; (b) 1882 less 1 1/4 equal 1880 3/4; and (c) 1911 less 1 1/4 equal 1909 3/4, and give the dates (a) October, 1874, (b) October, 1881 and (c) October, 1910, A. D.
How long this sifting of the consecrated will last, during which some will be granted the crowns of those adjudged unworthy, and their names written instead of some whose names will be blotted out (Rev. 3:5, 11), the Scriptures do not, so far as we have yet seen, indicate; but this date, 1910, indicated by the Pyramid, seems to harmonize well with the dates furnished by the Bible. Page 363 Thy Kingdom Come 1898 Edition
The four years from 1910 to the end of 1914, indicated thus in the Great Pyramid, will be quite sufficient for the extreme of all that trouble; for when it reaches its terrible climax it cannot last long ; and "Except those days should be shortened there should no flesh be saved."-Matt. 24:22 Page 364 Thy Kingdom Come 1898 Edition