539 BCE certainly becomes fuzzy as a end point for your crazy seventy yera hypothesis. This pivotal date is only famous for the end of the Babylonian Monarchy and the Babylonian World Power. When dates are abused and misused as you have done by your distortion of this date then they are robbed of their original and historical significance and sadly become fuzzy.
Daniel did not assume that the seventy years had ended at all, you need to read Daniel 9:2 and take your fuzzy, 'Elton John' glasses off. Daniel simply discerned from the Jeremiah that the duration of the devastations of Jerusalem would be 'seventy years' and this period was about to be fulfilled. Because of its anticipated fulfillment Daniel was moved to seek Jehovah in prayer that the restoration of all things would take place.
This agrees with the presentation of matters in Chronicles whereupon immediately after the mention of the seventy years and its significance, Ezra proceeded to describe the Return under the Persian Cyrus with no metion of Babylon ending the seventy years.
Methodology is the use and implementation of a method or the study of method, it is scholars that use this precise term in the of their research or thesis. Your period from 609 to 539 is fuzzy for several reasons, first of which is that your beginning is not universally accepted either as the beginning for the biblical 'seventy years' and for the end of the Assyrian World Power. Your period of 'seventy years' is simply a chronological accommodation and is not that Jeremiah's seventy years which was a period of exile-servitude-desolation. Your seventy years is elastic made to fit any current whim or fancy, stripped of any biblical significance. In short, your theory does not have a period of seventy years it only exists as number subtracted from two other numbers. A conjurers' trick to deceive the many.
The seventy years of Jeremiah belong to Judah marked by its servitude to Babylon, its exile in Babylon and its desolated state. Isaiah's seventy years for Tyre was a period of domination by Babylon but in its case its servitude did not amount to an exact period of seventy years as was the case with Judah. Haran does not have any significance as the Fall of Nineveh in 632 BCE marked the end of the Assyrian World Power.
It seems that you hate prophecy and do not believe in the end times of Daniel or in the words of our Lord in addressing what has become known as the Olivet Discourse. Your attitude is one of disbelief and scepticism and one wonders if you really believe in anything at all except your own theories based upon the Jonsson hypothesis.