It would appear that Coriantumr is the same man who is given as the last remaining Jaredite in the Book of Ether. While is "discovered" by the people of Zarahemla, it is not clear when this occurred, whether after in the land of Zarahemla, or earlier in their history.
The brief explanation of the events depicted on the stela all have counterparts on the various stelae from the later Classic period among the Maya, though the correspondence is not precise. There are ancestors present that provide the connection to the source of the right of rulership (Schele, Linda, and David Freidel. A Forest of Kings. New York, William Morrow and Company, Inc. 1990, p. 141). That Coriantumr as king would be the central figure is attested on so many stelae that references are almost not needed. Schele and Freidel discuss the stela for 16 named nobles (see the index under "stela").
The victory over another people is also frequently commemorated, but it is at this point that we have our difficulties with the putative "stela of Coriantumr." Not only is it nearly impossible to find a king who creates a stone monument to the defeat of his people, but we have unanswered the question as to who could have carved the stela if the people of Coriantumr have been vanquished. Carving a stela takes time and the dedication of resources to support the carvers. With the dissolution of the kingdom, Coriantumr would have had no means of providing the support, and would be unlikely to himself have been a carver (not to mention the inexplicable memorialization of his defeat).
I can offer only a single suggestion. Since we have the information on Coriantumr through Mosiah's inspired (perhaps not literal?) reading of the stone, we may have a prophetic/seer "reading" of the stone for information that was not directly written in the text of the stone itself. Mosiah would be using the stone as a base text, but expanding the "text" with the extra information about the end of the Jaredites.
The discussion of the Jaredites will be reserved for the commentary on the Book of Ether, as much more relevant information is found there. For the moment, it is sufficient to remember that the Jaredites fit into the time and space for the Olmec civilization of Mesoamerica. It must be clearly noted that this does not mean that the Olmec were the Jaredites, or that the Jaredites were the Olmec. Rather, it means that the Jaredites would have participated in the Olmec culture, and we may use that culture as a backdrop for understanding the Jaredite cultural milieu.