TD : The Proclaimers book says the change was made in 1944 for some strange reason.
The Proclaimers book says (pp. 632, 633) :
Later on, during the years from 1935 through 1944, a review of the overall framework of Bible chronology revealed that a poor translation of Acts 13:19,20 in the King James Version, along with certain other factors, had thrown off the chronology by over a century. [Footnote] This later led to the idea - sometimes stated as a possibility, sometimes more firmly - that since the seventh millennium of human history would begin in 1975, events associated with the beginning of Christ's Millennial Reign might start to take place then.
[Footnote] See "The Truth Shall Make You Free," [1943,] chapter XI; "The Kingdom Is at Hand," [1944,] pages 171-5; also The Golden Age, March 27, 1935, pages 391, 412. In the light of these corrected tables of Blble chronology, it could be seen that previous use of the dates 1873 and 1878, as well as related dates derived from these on the basis of parallels with first-century events, were based on misunderstandings.
The significance of 1944 was the footnote on p.171 of The Kingdom is at Hand :
IMPORTANT: In the book "The Truth Shall Make You Free", published in 1943, the chronology on pages 150,151 concerning the kings of Jerusalem, from Solomon's successor to Zedekiah, is based on the book of 2 Chronicles, chapters 12 to 36. This appears to show the reigns of those kings as successive, end to end. Actually, however, this was not so, as is plainly shown in the books of 1 and 2 Kings, which books give us a countercheck on the successors of Solomon by a comparison of these kings of Judah with the neighbor kings of the ten-tribe kingdom of Israel. The chronological TABLE OF CONTEMPORARY KINGS AND PROPHETS AND RELATED EVENTS, on the next four pages, shows how the books of 1 and 2 Kings give a more accurate check on the reigns of the kings of Judah than does 2 Chronicles.
Measured by 2 Chronicles, the period of kings from Saul to Zedekiah was 513 years . Measured by the more precise and detailed books of Kings, the period was actually 511 years, or 2 years less . This fact affects the chronology as a whole and pulls man's creation 2 years closer to A .D. 1 and gives it the date 4026 B.C., not 4028 B.C.
The following chronology shows the date of Jerusalem's destruction as in the year 607 before Christ. This recognizes the fact that the ancient reckoning of the vulgar year began in the fall. In other words, the vulgar year 606 B.C. really began in the fall of 607 B.C. As stated on page 239 (para. 1) of "The Truth Shall Make You Free": ''Inasmuch as the count of the Gentile 'seven times' began its first year at the fall of 607 B.C., it is simple to calculate when they end. From the fall of 607 B.C. to the fall of B.C. 1 is exactly 606 years. . . Hence from the fall of B.C. 1 to the fall of A.D. 1914 is 1,914 years."