Hi Lavendar,
The wts don't really have a rebuttal that anyone, certainly no one with any knowledge of ancient history, would find acceptable. I guess they rely on their followers simply accepting the watchtowers teaching on 607/587, rather than doing the kind of independent research that many on this board and elsewhere have done. Getting them to accept the evidence of history will most likely be difficult, knowing the importance of 607 in their chronology. If they accept the falseness of watchtower teaching on that date, they are virtually accepting that for their whole time as jws they have been part of a belief system built on falsehood. I feel that many who have spent their entire life as jws would have a hard time doing that, but good luck with what you are trying to do.
Linda