Welcome Nobleheart. 607/587 was one of my first topics to research as well. For someone who wasn't really trained how to do biblical research it was a real chore and eye opener. I am so glad I went through it.
Sounds to me like you are doing the right stuff. Good for you.
If you have the WT CDRom check out this quote from the Isaiah Prophechy book I:
Chapter 19, Page 253, paragraph 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.” (Isaiah23:15a) 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?.I changed a portion of the text red. When I first read this it just jumped out at me. I have found this information/admission/theory in no other WT publication (if anyone has please post the location).