Consistency is not a strong point of the wt, unless we are talking about their consistent prophecy failures.
Consider how they determine the 2520 years of the gentiles and arrive at 1914.
For the first part of the equation,to get 2520, they use 360 day years. They then magically apply that change to 365 day years for the time frame 607 to 1914.
It's like multiplying 2 lbs of potatoes by 3 kgs of potatoes and claiming you now have 6 pounds of potatoes.
Conversion is a thing in maths but the wt is hoping no one notices.