John Gill Commentary 2 Kings 15:11

"Now the rest of the acts of Zechariah, behold, they are written in the book of the chronicles of the kings of Israel." — 2 Kings 15:11 (ASV)

And the rest of the acts of Zachariah
During his six months' reign, and what he might do before in the interregnum:

behold, they are written in the book of the chronicles of the kings
of Israel :
for be they more or fewer, good or bad, they were all recorded there which were of any moment.