Charles Ellicott Commentary 2 Kings 14:23

"In the fifteenth year of Amaziah the son of Joash king of Judah Jeroboam the son of Joash king of Israel began to reign in Samaria, [and reigned] forty and one years." — 2 Kings 14:23 (ASV)

THE REIGN OF JEROBOAM II. IN SAMARIA
(2 Kings 14:23–29).

Reigned forty-one years. —According to the statement of this verse, Jeroboam reigned fourteen years concurrently with Amaziah, who reigned altogether twenty-nine years (2 Kings 14:2); and thirty-seven years concurrently with Azariah (2 Kings 15:8), so that he reigned altogether not forty-one but fifty-one years. (The discrepancy originated in a confusion of the Hebrew letters נא, fifty-one, with מא, forty-one.)