And remember that the first prophecy Jeremiah makes in chapter 25 is that Jerusalem and these surrounding nations--which he names in detail in the same chapter--will SERVE the king of Babylon 70 years. The 70 years would end when God brought punishment on Babylon itself. You can't argue that they continued to serve the king of Babylon for 2 more years after Babylon was defeated. They were serving the king of the Medes and Persians then.
Either way, nowhere does the Bible mention any year at all. That's the biggest problem with the whole setup.