Ethos - JW's only contend that it is 'likely' or 'probable' that they returned in 537 B.C.E, not that it dogmatically occurred. I don't have to prove that it definitely happened, I just merely have to prove that it is possible. Perhaps you should read up on logical fallacies and especially 'the burden of proof'.
JWs do have to dogmatically claim it, as that is the basis of 607.
The Watchtower has as much basis for 537 as it did for 536, which they used to say was the return, back when they said Jerusalem was destroyed in 606 (due to their incompetence in understanding the lack of a year 0).
"THE SEVENTY YEARS OF DESOLATION This brings us to the period of the desolation of the land, which lasted seventy years, and was ended by the restoration of its people from Babylon, in the first year of Cyrus, B.C. 536 ..." Studies In the Scriptures Series II - The Time Is at Hand p.51
The Watchtower always did, and continues to ignore facts, and make baseless claims in an effort to prop up a desired result.