John Wesley on 2 Kings 17:1

To reign - He usurped the kingdom in Ahaz's fourth year; but either was not owned as king, by the generality of the people; or was not accepted and established in his kingdom, 'till Ahaz's twelfth year. Nine - After his confirmation and peaceable possession of his kingdom: for in all, he reigned seventeen, or eighteen years; twelve with Ahaz, who reigned sixteen years, and six with Hezekiah.