According to Wikipedia, 609 BC was the year Assyria fell. Viewing Jeremiah from the standpoint of the world powers, it makes perfect sense that the 70 years would apply to Babylon's ascendancy as the Isaiah's Prochecy book stated, instead of applying to Jerusalem.
*** ip-1 chap. 19 pp. 253-254 Jehovah Profanes the Pride of Tyre ***
“She Must Return to Her Hire”
21 Isaiah goes on to prophesy: “It must occur in that day that Tyre must be forgotten seventy years, the same as the days of one king.” (Isaiah 23:15a) Following the destruction of the mainland city by the Babylonians, the island-city of Tyre will “be forgotten.” True to the prophecy, for the duration of “one king”—the Babylonian Empire—the island-city of Tyre will not be an important financial power. Jehovah, through Jeremiah, includes Tyre among the nations that will be singled out to drink the wine of His rage. He says: “These nations will have to serve the king of Babylon seventy years.” (Jeremiah 25:8-17, 22, 27) True, the island-city of Tyre is not subject to Babylon for a full 70 years, since the Babylonian Empire falls in 539 B.C.E. Evidently, the 70 years represents the period of Babylonia’s greatest domination—when the Babylonian royal dynasty boasts of having lifted its throne even above “the stars of God.” (Isaiah 14:13) Different nations come under that domination at different times. But at the end of 70 years, that domination will crumble. What will then happen to Tyre?
22 Isaiah continues: “At the end of seventy years it will happen to Tyre as in the song of a prostitute: ‘Take a harp, go around the city, O forgotten prostitute. Do your best at playing on the strings; make your songs many, in order that you may be remembered.’ And it must occur at the end of seventy years that Jehovah will turn his attention to Tyre, and she must return to her hire and commit prostitution with all the kingdoms of the earth upon the surface of the ground.”—Isaiah 23:15b-17.
23 Following the fall of Babylon in 539 B.C.E., Phoenicia becomes a satrapy of the Medo-Persian Empire. The Persian monarch, Cyrus the Great, is a tolerant ruler. Under this new rulership, Tyre will resume her former activity and try hard to regain recognition as a world commercial center—just as a prostitute who has been forgotten and has lost her clientele seeks to attract new clients by going around the city, playing her harp and singing her songs. Will Tyre succeed? Yes, Jehovah will grant her success. In time, the island-city will become so prosperous that toward the end of the sixth century B.C.E., the prophet Zechariah will say: “Tyre proceeded to build a rampart for herself, and to pile up silver like dust and gold like the mire of the streets.”—Zechariah 9:3.
Can it be any more plain? 609 BC Assyria fell to Baylon. 539 BC Babylon fell to the Persians. 70 years. For Babylon. And that understanding is exactly what is applied to Tyre. Different nation come under that domination at different times DURING the 70 years of Jeremiah, which applied to the period of Babylon's greatest dominion—NOT to Jerusalem's subjugation. According to celebrated WT scholars.
AuldSoul