70 was a number representing a lifespan. 7and 10 are also symbolic numbers used countless times. When Esarhaddon was moved to restore Babylon, after it was destroyed by his father, he references the belief that Marduke had decreed 70 years of desolation for their unfaithfulness, but due to his mercy he reduced it to 11 (70 upside down was 11 in their script). Interestingly enough even 11 wasn't literal either it seems he set to rebuilding it prior to that.
When in the reign of an earlier king there were ill omens, the city offended its gods and was destroyed at their command. It was me, Esarhaddon, whom they chose to restore everything to its rightful place, to calm their anger, to assuage their wrath. You, Marduk, entrusted the protection of the land of Assur to me. The Gods of Babylon meanwhile told me to rebuild their shrines and renew the proper religious observances of their palace, Esagila. I called up all my workmen and conscripted all the people of Babylonia. I set them to work, digging up the ground and carrying the earth away in baskets..."what was taken and plundered from Babylon, he has returned" and from Sippar to Bab-marrat the chiefs of the Chaldeans bless the king, saying, "(It is he) who resettled (the people) of Babylon"....Seventy years as the period of its desolation he (Marduk)
wrote down (in the book of fate). But the merciful Marduk in a moment his heart was at
rest (appeased) turned it (the book) upside down and for the eleventh year ordered its restoration.
The endless debates about what starting and ending points of a period that there is every reason to believe was a literary trope in lands controlled by Babylon just results in nothing but confusion and frustration.
Add to this the fact that Ezek 4:6 similarly uses the 40 year trope to indicate the same period.
Arguing about the number of angels that can dance on the head of a pin comes to mind.