The “Chronology” article in “Insight on the Scriptures” accepts from secular sources the date of 539 BCE for the Fall of Babylon. It must do so since it is not possible for pre-Christian sources to provide dates in terms of present-day calendars.
The “Chronology” article, however, denigrates the dates, source material, and chronologies employed by those who provide it with that date.
My study is available at:
http://www.jwstudies.com/Insight_s_reliance_on_secular_sources.pdf
Doug