I think the original quote above is probably from the Oct/Nov 2011 WT which was a two part discussion "proving" 607 BCE. As I recall it was written by Rolf Furuli whose academic work has long been discredited.
A couple of years ago he saw through the GB and wrote a book exposing them for which he was disfellowshipped.
There is a YouTube video that shows how to calculate Jerusalem's destruction was 586/7 using only WT sources.
George