Scholar says: The Wt literature has not made much mention of the secular materials as you suggest because these documents cannot establish a workable chronology of the OtT because these materials contradict the biblical seventy years.
Watchtower says:
18
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 (Note: To extend the list would be an easy matter, but it would only serve to further confirm a date not in question. ). 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.
"Cyrus entered Babylon in 539 B.C." (Encyclopœdia Britannica, 1946, Vol. 2, p. 852) "When Cyrus defeated the army of Nabonidus, Babylon itself surrendered, in Oct. 539, to the Persian general Gobryas."—Ibid., Vol. 6, p. 930.
"In 539 B.C. Babylon fell without a struggle to the Achaemenid Persian, Cyrus the Great."—The Encyclopedia Americana, 1956, Vol. III, p. 9.
"Babylon was captured by Cyrus in 539 B.C."—Yale Oriental Series · Researches · Vol. XV, 1929, Nabonidus and Belshazzar, Dougherty, p. 46.
"The Persians took the city in 539 B.C." (The World Book Encyclopedia, 1966, Vol. 2, p. 10) "In 539 B.C., the Persians conquered Babylonia." (Ibid., p. 13) "Nabonidus, the last king of Chaldean Babylonia, who reigned from 555 to 539 B.C."—Ibid, p. 193.
"The downfall of Lydia prepared the way for a Persian attack on Babylonia. The conquest of that country proved unexpectedly easy. In 539 B.C. the great city of Babylon opened its gates to the Persian hosts."—Ancient History, Hutton Webster, 1913, p. 64.
"In 539 B.C. Babylon, too, was captured by Cyrus."—The Story of the Ancient Nations, W. L. Westermann, 1912, p. 73.
"In 539 B.C., however, Cyrus advanced for the conquest of Babylonia. . . . Sippar was taken without a blow and, two days later, the van of the army of Cyrus entered Babylon."—History of the Hebrews, F. K. Sanders, 1914, p. 230.
"It is not likely that there was a long interval between his [Nebuchadnezzar’s] death and the fall of the Chaldean Empire before the onslaught of Cyrus in 539."—The Biblical Period, W. F. Albright, Reprinted from The Jews; Their History, Culture and Religion, edited by Louis Finkelstein, 1955, p. 49.
"Cyrus entered Babylon on October 29, 539 B.C. and presented himself in the role of the liberator of the people."—The Zondervan Pictorial Bible Dictionary, 1965, p. 193; see also pages 93, 104, 198, 569.
"Nebuchadnezzar had surrounded Babylon with huge walls, but after the defeat of Belshazzar’s army the city surrendered with slight resistance in 539 B.C."—World History at a Glance, Reither, 1942, pp. 28, 29.
"When the Neo-Babylonian Empire fell to the Persians, Babylon opened its gates to Cyrus in 539 B.C. without opposition."—The Interpreter’s Dictionary of the Bible, 1962, p. 335.
"In the seventeenth year of Nabonidus (B. C. 539), Cyrus captured Babylon."—The Popular and Critical Bible Encyclopœdia and Scriptural Dictionary, Fallows, 1913, Vol. 1, p. 207.
"Cyrus the Great, in 539 B.C., added the Babylonian to the other empires which he had acquired and consolidated with magical ease and celerity."—A New Standard Bible Dictionary, 1926, p. 91.
"The city [Babylon] was taken by surprise B. C. 539."—The Universal Bible Dictionary Peloubet, 1912, p. 69.
"539 B.C. marked the collapse of Semitic hegemony in the ancient Orient, and the introduction of Aryan leadership which continued for at least a thousand years. This conquest of Babylon by Cyrus laid the foundation for all the later developments under Greek and Roman rule."—Darius the Mede, Whitcomb, 1959, Introduction, p. 2.
"It was Cyrus, also, who conquered Babylon in the year 539 B.C. and thus became master of Mesopotamia and Syria."—Ancient and Medieval History, Hayes and Moon, 1930, p. 92.
"Nabonidus (Nabunaid) . . . was the last King of Babylon (555-539 B.C.)."—The Catholic Encyclopedia, 1907, Vol. 2, p. 184.
"In 539 the kingdom of Babylon fell to Cyrus."—The New Funk & Wagnalls Encyclopedia, 1952, Vol. 10, p. 3397.
"The Chaldean Empire, with its capital at Babylon (Second Babylonian Empire), lasted, . . . until 539 B.C., when it collapsed before the attack of Cyrus."—The Outline of History, H. G. Wells, 1921, p. 140.
"Cyrus conquered Babylonia in 539 B. C."—The International Standard Bible Encyclopœdia, 1960, Vol. 1, p. 367.
"In the year 539 Cyrus conquers the city Babylon, Babylonia becomes a province of the Persian Empire."—Translated from the German Bibel-Lexikon, edited by Herbert Haag together with associates, printed in Switzerland, in 1951. See page 150 under Babylonia.
steve