Jehovah's Witnesses: Was Jerusalem destroyed in 607 or 587 B.C.E?

The WTS claims that Jerusalem was destroyed in 607 B.C.E. and uses Dan 4:23-25, Rev 12:6, 14, Num 14:34, and Ezek 4:6 to come up with 1914 C.E., which is 2,520 years later, as the year that Jesus began his reign in heaven. If the WTS’s claim that Jerusalem was destroyed in 607 B.C.E. is correct, then why is it that every reference source, including the Encyclopedia Britannica, Microsoft Encarta, The World Book Encyclopedia, Encyclopedia Americana, Compton’s Encyclopedia, Acedemic American Encyclopedia, Cambridge Ancient History – Vol. III, The Oxford Dictionary of World History, etc, etc, all state that Jerusalem was destroyed in 586 BC? If the WTS is correct that Christ’s reign in heaven started 2,520 years after the destruction of Jerusalem, shouldn’t this event have occurred in 1935 instead of 1914? Should we view the overwhelming opinion of essentially every historian who is an expert on ancient history, or the WTS, as unreliable?