Ooh, eggie's back!
Another long-winded post, but your argument appears to boil down to this:
An inscription contained in the Nabonidus Chronicle reads: "Babylon fell VII/16/17," [It doesn't 'read' that way, but the information is taken from it. ~A] indicating that the date of Babylon's fall occurred on Tishri 16, 539 BC. ("VII/14/17" meaning: Tishri, the seventh Hebrew month, the 14th day, in the 17th year of Nabonidus' reign, wherein Belshazzar, as coregent, had ruled in Babylon since 556 BC.) Ezra 1:1-3 indicates that it was "in the first year of Cyrus the king of Persia" -- Cyrus' first regnal year ran from Nisan 538 BC to Nisan 537 BC -- that Cyrus caused a decree to go out to the Jews to "rebuild the house of Jehovah the God of Israel," which means that what the Nabonidus Chronicle tells us is that Cyrus' accession year occurred in 539 BC.
Since Ezra 3:1 indicates that it was "after seventy years" in the "seventh month" of Tishri 537 BC -- the same month in which the land of Judah suffered desolation "without inhabitant" living in any of the cities of Judah as had been foretold by the prophet Jeremiah -- that the repatriated Jews had returned to their cities (Jeremiah 25:11, 12; 29:10; 33:10), and Ezra 3:6 states that "from the first day of the seventh month," that is to say, on Tishri 1, 3225 AM, September 4, 537 BC, Julian, August 29, 537 BC, Gregorian, the repatriated Jews began to offer sacrifices at God's altar in Jerusalem. This means that this 70-year period would have come to an end on Tishri 1, 537 BC, following the commencement of Cyrus' first regnal year.
x = 537 BC
x = x (+ -70)
x = 607 BC
Thus, by subtracting 70 years from 537 BC, we can deduce based on (1) the Bible, (2) Josephus and (3) the Nabonidus Chronicle that the land of Judah had been made to lie desolate by Babylon on or about Tishri 1, 3155 AM, September 27, 607 BC, Julian, September 20, 607 BC, Gregorian, which is when this 70-year period would have commenced.
I'll c&p a post I made recently on another board to someone who made a similar argument.
The exiles were allowed to go home sometime in Cyrus' first year (Ezra 1:1). The problem is that the Bible does not specify WHEN in Cyrus' first year permission was given to the exiles to return to their homeland. Saying it must have been at the end of his first year (i.e. Winter/Spring 538/7 BCE to allow for a 537 BCE return) is really speculation. The Bible says the Jews were settled in their home towns by the 7th month (Sept./Oct.) (Ezra 3:1). Cyrus could equally have released them at the beginning of his first year (Spring 538 BCE), thereby enabling the Jews to be settled home by Sept./Oct. 538 BCE ...
... Or, Ezra may have even been counting Cyrus' accession year as his first year (October 539 BCE - Spring 538 BCE) which again, means the Jews would have been settled home by Sept./Oct. 538 BCE.
Either way, 537 BCE as the year the exiles' returned is a conjectured date.
Naturally, if the exiles returned in any other year than 537 BCE, it messes up your sum 537 + 70 = 607. Moreover, conjecture is not evidence.
Of course, there are the other matters that skew your perspective on this and have already been discussed earlier in this very long thread, namely, the fact that there continued to be inhabitants in the land some months after Gedaliah was assassinated (according to Ezekiel), and that the 70 years were not a period of uninhabited desolation of the land but (according to Jeremiah) a period of Babylon's domination over the nations.