Have you noticed that adding 607 B.C.E Roman/Gregorian years to 2520 Jewish biblical/prophetic years to get 1914 Roman/Gregorian years C.E is like adding 2 feet + 3 meters= 5 meters?
The insights volume II under heading year, mentions that a bible or prophetic year is reckoned to have 360 days. Many other publications indicate that a prophetic year is 360 days long. Thus the 2520 years have 360 days each. Despite that, they immediately add the 2520 prophetic years to Gregorian 607 B.C which each has 365.2425 days.
What should be done is first to express the prophetic period in terms of Gregorian years. This can be done by multiplying the 2520 years by 360 days, then dividing the product by 365.2425. That would give 2483.83 Gregorian years. These can then be added to Gregorian 607 B.C.E and the terminal date would not be 1914 but 1878 C.E! Jehovah's witnesses have made a math blunder by adding time that is expressed in two different units ! They keep teaching this to the world saying it is the basis for establishing that Jesus became king in 1914