So if you believe 607 is the year Jerusalem fell then you believe 629 is the year for the fall of Assyria, so do you understand that that means Babylon was ruling from 629-539, 90 years
So What, let chips fall where they may!!!'
Jeremiah 25:11 states that the nations would only have to serve Babylon 70 years, that's why we can say that 609 is the correct date for the fall of Assyria which would mean Babylon ruled from 609-539, 70 years and that also means that the fall of Jerusalem was in 587
Jer. 25:11 applies to Judah along with other nations or peoples that had to serve Babylon a full 70 years which ended after Babylon fell in 539 BCE for the following verse, v. 12 is now addressed to Babylon. So the focus has shifted from Judah as described from vs. 1-11 and shifts to Babylon as described in vs. 12-14 then from vss, 15-38 the judgement message is now addressed to the other nations.
So, the subject or focus of Jer. 25:11 is not any serving to Babylon but the Land of Judah as shown by the immediate context from vs.9. Also, the 70 years in some Bibles is mentioned at the beginning of the text rather than the end which helps the reader to get the sense of this text.