The jehovahs-judgement site is full of errors in logic, interpretation, and fact. The primary premise on that site, from which the rest is interpreted, is that the beginning of the 70 years MUST start with Jerusalem's destruction based on Jer 25:29 -- where the calamity begins with Jerusalem.
However, calamity is different than destruction of the temple and removal of Zedekiah. More importantly, if you search that verse on the Watchtower Library you will see that the WT interprets the calamity as beginning BEFORE the destruction of the temple.
That alone blows up much of the 'reasoning' on the site. Amazingly, Witnesses will use this site as a means of defending the 607 BCE date without realizing that it actually undermines the Society's interpretation.