The Revelation books clearly shows that the date 606B.C.E was believed to be the destruction of Jerusalem in the original JW doctrine.
When it was discovered that there was no year zero, this was changed to 607B.C.E. without question.
On page 105 the Revelation Book quotes:
Providentially, those Bible Students had not realized that there is no zero year between "B.C." and "A.D." Later, when research made it necessary to adjust B.C. 606 to 607 B.C.E., the zero year was also eliminated, so that the prediction held good at "A.D. 1914."
There was research that shows that the date was changed by one year. But no quotations from historians, no historical evidence provided. Just a statement.
So what was the evidence did they provide? Did they ever provide any?