en_tn_condensed/1ki/15/31.md

are they not written in the book of the events of the kings of Israel?

This question is used to either inform or remind the readers that the information about Nadab is in this other book. See how you translated a similar phrase concerning Judah in 1 Kings 14:29. This rhetorical question can be written as a statement. AT: "they are written in the book of the events of the kings of Israel." (See: rc://en/ta/man/translate/figs-rquestion)

are they not written in the book of the events of the kings of Israel?

This can be stated in active form. AT: "someone has written about this in the book of the events of the kings of Israel." (See: rc://en/ta/man/translate/figs-activepassive)