Social: The letter comes form the “leader and the governor” of the Gadiantons. It is addressed to Lachoneus, who is “governor of the land.” This parallelism of phrases suggests that Lachoneus and Giddianhi hold similar positions. This would be true if both were the leader in a city-state that had subsidiary or beholding cities. We know that this is the case for the land of Zarahemla, and everything we can glean from the text indicates that the Gadiantons are similarly a city-state with beholding cities. Thus we have a high level communication from one governor to another.
Textual: Mormon has included the text of a letter. This would have been copied into the Nephite record, and as it began as a written document, the probability is high that we have an accurate copy. The only issue with this letter is the nature of translation, not the source itself. This is one of the rare prime sources in Mormon’s text.