There's a very good question to stump a JW(hope I have spelled the place right?!)
It says in my NIV study Bible it toke place c.609 BC so therefore the Fall Of Jerusalem toke place approxiametly(sic)20 years later according to the Bible.
If you say Carchemish toke place in 627,`can you provide evidence of this?' might be a good question to a JW.