פירוש על מלכים ב 15:30

In the twentieth year of Yosam. He should have said, “in the fourth year of Achaz,” because Yosam's entire reign lasted [only] sixteen years, but since Achaz was wicked, Scripture prefers to count [the years with reference] to Yosam who was in the grave, rather than to Achaz, who was alive.¹³Alternatively, because the Divine decree of destruction had been passed against Pekach during Yosam's reign, therefore its fulfillment is reckoned in terms of his reign even though it took place after his death.—Radak Thus it is [stated] in Seder Olam.