Hi Doug. (Sorry to hear about your wife's illness. I know this is a life experience you're going through and its different for everyone. I wish you strength and comfort to get through this. My parents are aged and ailing and it certainly reminds of how short life can be and renews our reason for hope in a better world).
It is not possible for the WTS -- or anyone else for that matter -- to prove which year the Jews returned to Jerusalem following the decree by Cyrus.
It is not possible to show that this is the event that marked the end of the "70 years of servitude" by the nations listed by Jeremiah.
Doug, it is porbably not "possible" to prove anything in the ancient past. But we can confirm and examine the various references that survive that are pertinent to the issue. In this case:
1. Ant. 11.1.1 by Josephus confirms that HIS interpretation of Jeremiah's prophecy was fulfilled when the "people went off their land" meaning at the time of the last deportation, thus the 70 years are from year 23 of Nebuchadnezzar to the 1st of Cyrus. That is the "subjective" chronology.
2. The VAT4956 contain two date references for year 37 of Nebuchadnezzar: one in 568 BCE and one in 511 BCE. The double dating though, explains the reason for the "diary" in the first place, which was just to hide reference to the original chronology. So the most academically correct chronology via the VAT4956 for the true dating for the NB Period dates year 37 of Nebuchadnezzar to 511 BCE. It is only this date that a Bible scholar would be thus interested in comparing with the Biblical timeline. This dating would date year 23 to 525 BCE and thus the 1st of Cyrus is corrected by the VAT4956 to fall in 455 BCE. Since 455 BCE works as the year the "word goes forth to rebuild Jerusalem" which is a pivotal date fulfilling the 70 weeks prophecy where the messiah's baptism in 29 CE establish the beginning of this prophecy, you have the OPTIONAL alignment of the Bible's timeline with the VAT4956 confirmed original NB dating. 607 BCE and 587 BCE are considered incompetent dates belonging to the revised timeline.
So true, no one can CONFIRM 455 BCE as the correct dating for the Jews return from Babylon, but it is the most academically correct dating at this point, and it is the Biblically correct date. Now, I've reporeted on the VAT4956. It's not my fault if people don't understand astronomy enough to know there is no further choice here.