Historical: Mormon uses this next section to create some moral balance in the Nephite history. The Amulonites were apostate Nephites, and responsible for the death of Abinadi. Mormon makes these things “right” by noting the final disposition of the Amulonites. First, we have many of them killed by Nephites. This “balances” the apostasy by having the Nephites exact a form of justice upon them.
The historical problem with this entire section is the dubious nature of the possible sources for this information. It is unlikely, though perhaps possible, that the Amulonites would wear some mark that identified them as Amulonites so that they might be counted separately in the casualties of war. That could possibly account for Mormon’s ability to say that many Amulonites had been killed, but certainly not a statement like “almost all the seed of Amulon….”
Indeed, it is hard to see where Mormon is going to get an authentic source for any of this information. It is most probable that he is basing this information on tradition rather than text. The nature of the balancing of scales with the Amulonites, and the final indication that their descendants were still hunted are all aspects which seem to suggest a traditional tale here rather than a document. As with many traditional tales, the balancing aspects may have been more important than historical fact. As a moral tale, this section has value. As history, it is suspect.