The weight of evidence against 607BCE is indeed immense and largely undisputable, and I reckon that the Society know this only to well. My theory is they will let the old battered chronology of the "seven Gentile Times" slip away gradually or they will continue to hold to this untruth to their detriment.
If you are a baptized Witness, any further letters disputing the "accepted chronology" could cause you trouble in the long run as they will begin to treat you the same way as they treated Carl Olaf Jonnson who wrote The Gentile Times Reconsidered. Letters from the Branch Office will be couched in love and concern for your spiritual welfare but the truth is they will want to silence you and "protect the flock". They may already suspect you of reading "apostate" literature by raising the subject in the first place.
Regarding any further correspondence with the Society, I would certainly err on the side of caution. Part of you may want to "sock it to em", I know, I have also felt that way, but with closed minds your research, however true will usually be rejected as "running ahead of the organization/Jehovah." My guess is that accurate Biblical research that is sent in to the Branch Office is not taken seriously unless you are of a high rank and preferably one of the "anointed". You may hope that the Society may turn around suddenly and send you a letter to the effect that "we accept your findings and will announce the truth of the matter at our next
district convention, but,this miracle has yet to happen.
The knowledge that you have acquired on 607 (and probably other matters) brings with it responsibility. You may feel obliged to speak up for truth, and this is commendable, but you also run the risk of being disfellowshipped and losing any friends you may have in your congregation. So my advice would be to to leave it as a matter of prayer, because God know's best and he will guide your conscience in the right way. I would also ask you to pray that he will reveal the correct path to others that have a responsibility to speak out for the truth - the Governing Body of Jehovah's Witnesses.
Regards
Steven