Chronology/ Redaction: The fifteenth year of the reign of the judges would be approximately 79 B.C.
We have three recorded dates for two military actions. The first date (Alma 16:9) tells us that the destruction of Ammonihah takes place in the eleventh year of the reign of the judges. After three years of peace, the Lamanites return in the fourteenth year (Alma 16:12). That battle is the same that Mormon has just described, ending in the fifteenth year of the reign of the judges.
This span between the fourteenth and fifteenth year might suggest that the war lasted an entire year, but that is unlikely. The logistics of supplying an army increase exponentially with time. Both armies would require food. A year-long war would not allow attackers or defenders to plant and harvest. Rather, we have a “missing year” between the attack that comes in the fourteenth year and the war’s conclusion in the fifteenth year.
The battle almost certainly terminated before the end of the fifteenth year because Mormon describes the period of mourning prior to closing the year’s record. What we do not know is how much before the year’s end the battle ended. The question may be irrelevant, however, since Mormon’s source seems to have been created year by year. Within that year, I suspect that Mormon may not have taken pains over the timing of events, probably because this approach was not relevant to Mormon, given his distance from the events and his purpose—religious, rather than historical. While we might seem to have a missing year, I would argue that it is most easily explained by Mormon’s editorial approach.