Molina, in the 1555 edition of his vocabulario, notes a difference between cecentetl and cecen. The first means "a cada cosa redonda," and the second means "a cada cosa no redonda." The implication is that the "tetl" addition suggests something round, like a stone, and not just a counter/unit. See f. 2v.
Frances Karttunen:
CĒCENTE-TL one apiece, one for each / cada uno sendos, o a cada uno sendos, o a cada uno de los (M) redup. CENTE-TL Frances Karttunen, An Analytical Dictionary of Nahuatl (Norman: University of Oklahoma Press, 1992), 27.