This is just my opion, but It seems clear to me, that 70 years refers to the totality and 50 years just for the
the temple. I try not to read between the lines. But I have learned to never assume I'm correct. I think
joesephus would have realized that he had two different time lines there. Or even in his time someone
would have pointed it out to him.
You should realize that these historians had to walk the political line. If they told the truth they wouldn't get published. So the solution was to write something politically correct and hide details of the original chronology. Thus a lot of the original events are hinted at in the historical works that survive. Josephus was very adept at it and he definitely knew the revised and the original chronology.
For instance even Against Apion 1.21 is suspicious for giving away the events at Babylon during the 20 years of Cyrus reign claiming to be a reference to the siege of Tyre for 13 years beginning year 7 of Nebuchadnezzar.
Why?
Because if you begin a count of 13 years from year of Nabonidus it ends up matching the fall of Babylon. He claims someone became a king in year 14. Plus, "Hiram" was someone during the time of Nebuchadnezzar, sort of a hint there is something hidden. That reference thus prevents us from excluding that Josephus didn't know the precise chronology of the NB Period. Even in his antiquities he gives us an 18-year for Evil-Merodach, later changed to just 2 years in Against Apion.
The corrected history has Cyrus ruling for 20 years beginning the 6th year of Nabonidus. That is based on Babylonian records. If so the period from the 1st of Nabonidus to the 1st of Cyrus over Babylon is a 25-year period. We know from the Bible that Darius the Mede ruled for six years and thus Nabonidus's original rule would be 19 years (25 minus 6 = 19). Cyrus rules for 21 years inclusive down to his rule in Babylon starting with year 6. But if you begin the 20-year count from year 7 then the 20th year will be the 1st of Cyrus at Babylon. That's a 19-year period. 19 minus 6 years for Darius the Mede leaves 13 years, the number of years Josephus claims Tyre was under siege. But it would also be the number of years from year 7 of Nabonidus that Babylon would fall in his 19th year. So if you want, Josephus confirms that he knew Darius the Mede ruled for 6 years and the precise Babylonian timeline.
There are other examples in the works of the other revisionists. I'll give you two of my favorites!
LS