Verse 9 teaches us something about how Mormon is using the name Gadianton in his text. Giddianhi is the leader and declares that he is the governor over this group that Mormon has called Gadiantons. Mormon has Giddianhi declare that he is the governor “of this the secret society of Gadianton.” The way Mormon uses the name Gadianton suggests that the name is probably something Mormon has added to the letter. The purposes for which Mormon is using the name also tell us why Giddianhi declares that he leads a “secret society.”
When one puts into a political letter that they lead a “secret society,” it stretches the imagination to see it as “secret.” In this case, Giddianhi uses the name and description for intimidation factor. A society that is truly secret could not be intimidating, because no one would know about it.
What we are seeing is Mormon using the Nephite historical record to teach the lesson from history that his future readers need to know about. Mormon has declared that the Gadiantons will be the force that destroys the Nephites in Mormon’s day (see Helaman 2:13). He is setting up his readers understanding of the dangers of that society, and linking them to the secret societies that destroyed the Jaredites.
This light manipulation of history should not be thought of as Mormon being inaccurate, or that there is anything wrong with the translation of the text. This is the same type of history that we see in much of the Old Testament, where historical events are used as the foundation for the stories that would educate the readers. It is a sign that the Book of Mormon follows ancient canons of how history should be used, rather than those of the more modern society in which Joseph Smith lived.