The book babylon the great was published in 1963 and you left out the fact that that statement was a direct quote from the Encyclopedia Americana Vol 2; page 441 not our own interpretation
Insight on the Scriptures (more recently published) information is the same as what you will find on Wikipedia. Interestingly more information (since the 1963 publication sited above) has come available, for instance:
Paul-Alain Beaulieu is a Canadian Assyriologist, a Professor of Near and Middle Eastern Civilizations at the University of Toronto. He subsequently translated the The Nabonidus Cylinder and was the author of the book The Reign of Nabonidus, King of Babylon, 556–539 B.C. (Ph.D. thesis, Yale University, 1989, and Yale Near Eastern researches 10, Yale University Press, 1989, ISBN 9780300043143)..... More on wikipedia
The Watchtower quote is only a partial piece of information which says "other investigators say this". We are not the other investigators, just quoting a fair assessment of different literary works. If you actually weren't just looking at Jehovah's witness hate site who twist information to discredit us, you may have seen the rest of the information that says:—Brown University Studies, Vol. XIX, Babylonian Chronology 626 B.C.—A.D. 75, Parker and Dubberstein, 1956, p. 13. Recognized authorities of today accept 539 B.C.E. without any question as the year Babylon was overthrown by Cyrus the Great. In addition to the above quotations the following gives a small sampling from books of history representing a cross section of both general reference works and elementary textbooks. These brief quotations also show that this is not a date recently suggested, but one thoroughly investigated and generally accepted for the past sixty years. END QUOTE
The Bible shows that Jehovah enables his servants to understand his purpose in a progressive manner. (Prov. 4:18; John 16:12) Thus, the prophets who were divinely inspired to write portions of the Bible did not understand the meaning of everything that they wrote. (Dan. 12:8, 9; 1 Pet. 1:10-12) The apostles of Jesus Christ realized that there was much they did not understand in their time. (Acts 1:6, 7; 1 Cor. 13:9-12) The Bible shows that there would be a great increase in knowledge of the truth during “the time of the end.” (Dan. 12:4) Increased knowledge often requires adjustments in one’s thinking. Jehovah’s Witnesses are willing humbly to make such adjustments.
Perhaps you could write to the people who actually wrote these reference works to tell them. Here is a list for your reference:
Encyclopedia Britannica, 1946, Vol. 2, p. 852 bid., Vol. 6, p. 930.
The Encyclopedia Americana, 1956, Vol. III, p. 9.
Yale Oriental Series ‧ Researches ‧ Vol. XV, 1929, Nabonidus and Belshazzar, Dougherty, p. 46.
The World Book Encyclopedia, 1966, Vol. 2, p. 10; Ibid., p. 13; Ibid, p. 193.
Ancient History, Hutton Webster, 1913, p. 64.
The Story of the Ancient Nations, W. L. Westermann, 1912, p. 73.
History of the Hebrews, F. K. Sanders, 1914, p. 230.
The Biblical Period, W. F. Albright, Reprinted from The Jews; Their History, Culture and Religion, edited by Louis Finkelstein, 1955, p. 49.
The Zondervan Pictorial Bible Dictionary, 1965, p. 193; see also pages 93, 104, 198, 569.
World History at a Glance, Reither, 1942, pp. 28, 29.
The Interpreter’s Dictionary of the Bible, 1962, p. 335.
The Popular and Critical Bible Encyclopœdia and Scriptural Dictionary, Fallows, 1913, Vol.1,p. 207.
A New Standard Bible Dictionary, 1926, p. 91.
The Universal Bible Dictionary Peloubet, 1912, p. 69.