JWs are correct about 607 and 1914. Somewhat. The theory behind it is that Jehovah told David that his offspring would sit on Jehovah's throne forever culminating in Jesus. But when Jesus was on earth he didn't become king. Infact at that time, David's offspring were no longer in power on Jehovah's throne. Did Jehovah's statement fail?
No, it was paused. The kings in the line of David lost power when they became subject to another government. That happened in 607. In 587 Jerusalem was destroyed. 11 years prior, in 598, Zedekiah became king. 11 years and months prior to that in 610, Jehoiakim became king. Daniel said that 3 years after that, 607, captives were taken. Thus 607 is when the kings in the line of David lost sovereignty for 2520 years until 1914 when Jesus became king.