Its been said many times but for new ones I'll mention again that ' 70 years' was a motif, a recurring symbol of a period of punishment by the gods. It may well represent a generation. It was not literally meant to be counted 70 actual years. For examples Ezk. 23 proclaimed Tyre would be punished this 70 years but also said it would last forever, this thread and the linked one demonstrate that various OT passages used the 70 year motif in slightly different ways having different beginning and ending times, even in a Babylonian text the 70 year motif occurs, note:
"Seventy years, the reckoning of it's destruction which He had inscribed, the merciful God Marduke, as soon as his heart had calmed down, reversed the order (of the sign) and ordered it's resettlement after eleven years." Babylonian Inscription of Esarhaddon
The actual time the Jewish elite were in exile was 49-50 years. The farmers and peasantry never left but continued to work the land as subjegated people do. The book of Daniel calls this time 7 weeks (49 years) in the authors expansion of the older texts. He turned 70 years into 70 weeks (x 7 as per Lev 26:21) to salvage the prophecies.
Many on this board have correctly shown that the WTS spin on these passages is hoplessly flawed but then make the mistake of trying to locate a literal 70 years as some sort of fullfillment. To do this requires rather subjective often arbitrary starting and ending points which themselves ignore the various uses of the motif in the OT.