MeanMrMustard when I read in the Bible of 70 years of servitude of the nations to Babylon, I don't presume that means all the listed nations begin their 70 years of servitude in the same year. My impression is Babylon did not begin all of their invasions of the nations in the exact same year. Likewise Persia/Iran did not conquer all parts of Babylon in the same year and thus did not end in the exact same year the control of Babylon over various nations (at least to my knowledge). Thus, I don't presume that the servitude of all of the listed nations ended in the exact year. [However Jeremiah 25:12 gives the impression that the 70 years ends at the same time for the servitude of all of the listed nations to Babylon, and that Babylon's dominance (starting with king Nebuchadnezzar) last for exactly 70 years.]
I have very little interest (practically no interest) in the military battles Babylon had with various non-Jewish nations. But I do have some interest in the military battles and the timing of the degree of control that Babylon had with Jerusalem and Judah. The latter is case for me because the latter involves the Jews, and the Jews wrote the Hebrew Scriptures Bible (and much of the NT), and the Bible makes predictions of Yahweh's messianic kingdom upon "David's throne", and my life has been greatly influenced by the Bible. I thus focused my thoughts about Jeremiah chapter 25 upon Jerusalem and Judah.
Your (and another person's) emphasis (in posts from days ago) upon the word "servitude" (in regards to servitude of the nations) versus "desolation" influenced me to change my focus from the wording of "desolation" to the wording of "servitude". After I did that I noticed that certain verses in Jeremiah chapter 25 were primarily talking about servitude instead of desolation. I also read online that archaeology reveals that Judah was not totally desolate at any time during the Babylonian occupation of Judah (despite what Jeremiah 25:11, 18 says). [That makes sense since empires benefit by some people being allowed to remain in their native land, and thus work the land and pay taxes for the benefit of the empire. What emperor hungry of expansion of territory (and to rule people) would want much of his acquired lands to be without human subjects and to be desolate for decades? I don't think any would.]
As result I began seeing that the idea of Jerusalem and Judah being in servitude for 70 years (or very close to that number of years) is consistent with both the Bible and history and science (archaeology) and approximately with the date of 606 BCE, and that stunned me and greatly impressed me. After that, when I read Jamieson's commentary which gave the interpretation of Jerusalem's servitude having begun in 606 BC I thought its reasoning made a great deal of sense, and displayed no "tortured logic" in that matter. It also got around the issue of the fact that Jerusalem's destruction happened in the year 587 BCE (plus of minus one year) and revealed that the WT's reasoning about he the year 607 BCE (originally the year 606 BC) had some degree of logic and suitability to it. Regarding the idea of the Bible having prophesied that Judah would be desolate (instead of in servitude) for specifically 70 years, I don't recall any verses saying such, however I have not looked to see if there are any say such verses. In the past I might have read such verses, but I don't remember having read such. I do remember that the WT says that the Bible says that Jerusalem and Judah would be (and/or was) desolate for specifically 70 years, but I am not certain that view of the WT is correct. I am not 'defining the "desolation" referred to in v18 as more of a soft desolation, like a vassal or servitude.' I am not defining "desolation" as meaning "servitude"; to me they have very different meanings. I am not equating 70 years of servitude with seventy years of desolation. Likewise I don't see the Jamieson commmentary (which I quoted from) referring to the 70 years as soft desolation or any other desolation. That which I quoted from in it, in regards to the seventy years, is stated by the commentary as referring to the years of servitude and of captivity. I don't see it as saying the desolation as having lasted 70 years. It specifically says "Jeremiah's seventy years of the captivity begin 606 B.C.,
eighteen years before the destruction of Jerusalem ...."
I notice you said "Why start it at the first Exile of Judah when Neb had been marching around making vassals of other nations round about for years prior? Why reduce 'nations' to 'nation'?" But, I don't see the logic of that if by the first exile you mean the one which some commentaries say began in 606 BC (instead of in 587 BCE +- 1 year), since the Jamieson commentary which says the first deportation (claimed to be in 606 BC) began in the first year year of Nebuchadnezzar II's reign. The defeat of Pharaoh Necho II in a battle was in 605 BC (according to various sources I read, including commentaries and https://en.wikipedia.org/wiki/Nebuchadnezzar_II ). The plain sense of Jeremiah 25:29 says the calamity begins (starts) first with Jehovah's city (namely Jerusalem) and Judah and proceeds to gentile nations. Jeremiah 25:17-19 lists Jerusalem and Judah first and it lists "Pharaoh the king of Egypt" second. That sequence agrees with the historical record. I thus am not reducing " 'nations' to 'nation' ".
Though Assyria was conquered by Nebuchadnezzar II of Babylon before the year 606 BCE, Nebuchadnezzar II was not yet king at that time. Nebuchadnezzar II conquered Assyria while Nebuchadnezzar's father was king of Babylon (see https://en.wikipedia.org/wiki/Nebuchadnezzar_II ). I am convinced that the prophecy of Jeremiah chapter 25 pertaining to conquests by "Nebuchadnezzar the king of Babylon" (see verse 9) starts after Nebuchadnezzar II (historically known as Nebuchadnezzar the Great) became king. Note that Jeremiah 25:9 (1984 NWT) says "... to Nebuchadnezzar the king of Babylon ..." As a result, the conquest by Nebuchadnezzar II upon Assyria is excluded from the prophecy of Jeremiah chapter 25, since Nebuchadnezzar II was not yet the king of Babylon! [Perhaps the "prophet" Jeremiah learned of Nebuchadnezzar II's defeat of Assyria and from that knowledge then deduced by naturalistic means (instead of by a divine revelation from Yahweh) that Nebuchadnezzar II would become king and subdue Jerusalem, Judah, and Egypt and various other gentile kingdoms around Judah.] Also, note that the lists of kings/kingdoms mentioned Jeremiah 25:17-26 does not specifically name Assyria!
https://en.wikipedia.org/wiki/Nebuchadnezzar_II says the following.
'Despite his successful military career during his father's reign, the first third or so of Nebuchadnezzar's reign saw little to no major military achievements, and notably a disastrous failure in an attempted invasion of Egypt. These years of lacklustre military performance saw some of Babylon's vassals, particularly in the Levant, beginning to doubt Babylon's power, viewing the Neo-Babylonian Empire as a "paper tiger" rather than a power truly on the level of the Neo-Assyrian Empire. The situation grew so severe that people in Babylonia itself began disobeying the king, some going as far as to revolt against Nebuchadnezzar's rule.
After this disappointing early period as king, Nebuchadnezzar's luck turned. In the 580s BC, Nebuchadnezzar engaged in a successful string of military actions in the Levant against the vassal states in rebellion there, likely with the ultimate intent of curbing Egyptian influence in the region. In 587 BC, Nebuchadnezzar destroyed the Kingdom of Judah, and its capital, Jerusalem. The destruction of Jerusalem led to the Babylonian captivity as the city's population, and people from the surrounding lands, were deported to Babylonia. The Jews thereafter referred to Nebuchadnezzar, the greatest enemy they had faced until that point, as a "destroyer of nations". The biblical Book of Jeremiah paints Nebuchadnezzar as a cruel enemy, but also as God's appointed ruler of the world and a divine instrument to punish disobedience. Through the destruction of Jerusalem, the capture of the rebellious Phoenician city of Tyre, and other campaigns in the Levant, Nebuchadnezzar completed the Neo-Babylonian Empire's transformation into the new great power of the ancient Near East."