The list of Babylonian kings in the book “Babylon the Great Has Fallen” (BF) agrees with the secular records. (This might have been the material I queried the WTS about in 1963/64, but at the moment I am not certain.)
“Amel-Marduk (Evil-merodach) … succeeded Nebuchadnezzar. … After reigning but two years King Evil-merodach was murdered by his brother-in-law Neriglissar. According to the inscriptions that have been found, this usurper of the throne … reigned four years. When he died, his son Labashi-Marduk … succeeded him … and within nine months he had his throat cut by an assassin. Nabonidus … now took the throne and had a fairly glorious reign till Babylon fell in 539 BCE.” (BF, pages 183, 184).
(The words that I removed in the above quotation do not affect the meaning of any sentence, nor the overall meaning. I removed them to make the chronological information clearer.)
In 1988, the WTS again provided this sequence of kings: “Nabopolassar, a native of Chaldea, and his successors, Nebuchadnezzar II, Evil-merodach (Awil-Marduk), Neriglissar, Labashi-Marduk, Nabonidus, and Belshazzar, ruled the Third World Power, Babylon.” (“Insight on the Scriptures”, Vol 1, page 425, art.: “Chaldea”).
The WTS thus does not add any monarch to the accepted list, so their extra 19 or 20 years must be taken care of by stretching the reign of a king or two.
The WTS consistently agrees that Nebuchadnezzar reigned for 43 years. So the only way they could stretch the length of the neo-Babylonian dynasty would be to lengthen the reign of one or more of Nebuchadnezzar’s successors. The WTS writes that Evil-merodach reigned for two years and Labashi-Marduk for less than a year. This leaves Neriglissar and Nabonidus.
The WTS tries to cast doubt on the 4 years assigned to Neriglissar and it never assigns a length to the reign of Nabonidus.
The accepted chronology is supported by absolutely tens of thousands of dated clay tablets. Each tablet is dated according to the year of the monarch’s reign. Not one tablet has been found that is dated beyond the 4th year of Neriglissar or the 17th year of Nabonidus, let alone assigning an extra 20 years to either or in combination.
In 1956, an undamaged tomb inscription to the Mother of Nabonidus was uncovered that confirms the secular neo-Babylonian chronology starting with Nabopolassar (predecessor of Nebuchadnezzar) down to the 9th year of Nabonidus:
“From the 20th year of Ashurbanipal, king of Assyria, when I was born, until the 42nd year of Ashurbanipal, the 3rd year of his son Ashur-etil-ili, the 21st year of Nabopolassar, the 43rd year of Nebuchadnezzar, the 2nd year of Awel-Merodach, the 4th year of Neriglissar, during (all) these 95 years …
“From the time of Ashurbanipal, king of Assyria, to the 9th year of Nabonidus, king of Babylon, the son whom I bore, (i.e.) one hundred and four happy years …
“The 21 years in which Nabopolassar, the king- of Babylon, the 43 years in which Nebuchadnezzar, the son of Nabopolassar, and the four years in which Neriglissar, the king of Babylon, exercised their kingship, (altogether) 68 years.” (ANET, Pritchard, page 561). The WTS has known about this undamaged tomb inscription for over 50 years.
This inscription shows that Neriglissar reigned for 4 years. So the WTS’s only explanation would be to extend the reign of Nabonidus by 20 years. But this is denied by authorities the WTS relies on, such as Parker and Dubberstein’s “Babylonian Chronology 626 B.C.—A.D. 75” and others.