Before the Book of Mormon prophet Jacob popularized the terms Nephites and Lamanites to refer to the two Book of Mormon peoples, various names were used to refer to the peoples.
>”Now the people which were not Lamanites were Nephites; nevertheless, they were called Nephites, Jacobites, Josephites, Zoramites, Lamanites, Lemuelites, and Ishmaelites.” (Jacob 1:13)
So why isn’t Sam listed? Jacob and Joseph are. Laman and Lemuel are. All of Nephi’s brothers are except for Sam.