John Gill Commentary 1 Kings 15:9

"And in the twentieth year of Jeroboam king of Israel began Asa to reign over Judah." — 1 Kings 15:9 (ASV)

And in the twentieth year of Jeroboam king of Israel reigned
Asa over Judah .
] How this is to be accounted for (See Gill on 1 Kings 15:2).