@BB
Correct me if I'm wrong but I think Russell began with 607 because the walls began to be rebuilt in 537. Count back 70 years of God's predicted punishment and you arrive at 607 for the destruction of Jerusalem.
Once they had the 607 date then they used the 7 times of Dan 4 as you said to arrive at 1914.
But the 70 years were actually predicted years of servitude to Babylon and not of Jerusalem's destruction although during the years of servitude the city was destroyed and that as all non WT historians agree, took place in 587
So the WT calculations are all conjecture and theory which no real Bible scholar would support.