2Ki 24:8 Jehoiachin was eighteen years old when he became king, and he reigned three months in Jerusalem. His mother’s name was Nehushta the daughter of Elnathan of Jerusalem.
2Ch 36:9 KJV Jehoiachin was eight years old when he began to reign, and he reigned three months and ten days in Jerusalem: and he did that which was evil in the sight of the LORD.
Jehoiachin was, according to KJV, eight years old. The parallel passage, 2 Kings 24:8, in which he is described as 18 years old is obviously to be preferred; an eight-year old could hardly be described as doing evil as king.
2Ki 8:26 Ahaziah was twenty-two years old when he began to reign, and he reigned one year in Jerusalem. His mother’s name was Athaliah; she was a granddaughter of Omri king of Israel.
2Ch 22:2 KJV Forty and two years old was Ahaziah when he began to reign, and he reigned one year in Jerusalem. His mother’s name also was Athaliah the daughter of Omri.
Ahaziah was, according to the KJV, 42 years old. However most translations read 22 years old. This is not only to agree with 2 Kings 8:26, but also agreeing with some other manuscripts.
2Sa 10:18 And the Syrians fled before Israel, and David killed of the Syrians the men of 700 chariots, and 40,000 horsemen, and wounded Shobach the commander of their army, so that he died there.
1Ch 19:18 And the Syrians fled before Israel, and David killed of the Syrians the men of 7,000 chariots and 40,000 foot soldiers, and put to death also Shophach the commander of their army.
Should it be 700 or 7,000 chariots? Obviously one of the numbers has been corrupted in transcription.
To these verses I could add one in which the number is missing:
1Sa 13:1 Saul was … years old when he began to reign, and he reigned … and two years over Israel.
By quoting these verses together it might seem that many, perhaps most numbers in Kings and Chronicles have been incorrectly transcribed. This overlooks the fact that most of the numbers have been strongly supported to be correct by the work of Edwin R. Thiele. In his 1951 book “The Mysterious Numbers of the Hebrew Kings”, Thiele was able to reconcile the various lengths of the reigns of the kings of Israel and Judah with very few assumptions that there were transcription errors. He has done this by the use of co-regencies, a device in which a king would appoint his son to the throne sometimes many years before his death in order to secure his succession, as well as an understanding of how the years were counted differently in the northern and the southern kingdom, and at different times.
It also notable that the text was held in such respect by the Hebrew scribes that, although it was obvious in some cases that there was an error, they did not attempt to correct it, but conscientiously transcribed the text as they found it. This is just as well; I would far rather have the texts as they found them rather than as they thought they should be.
None of this answers your actual question, why God allowed these transcription errors to arise. Equally, though, we could ask why God should be bound by our desire for everything to be neat and tidied up. The purpose of scripture is given:
2Ti 3:16-17 All Scripture is breathed out by God and profitable for teaching, for reproof, for correction, and for training in righteousness, (17) that the man of God may be competent, equipped for every good work.
Would the scripture have been any more profitable for training in righteousness if transcription errors had not arisen? I think not.
(Unless otherwise stated I have quoted from the ESV Bible)