If the people of Limhi were "supposing" that Ammon and his brethren were priests of Noah (Mosiah 21:23), then presumably enough time had elapsed that either young people had grown up not knowing about the priests or the priests had grown older and thus were not recognizable, or both. It is not clear whether Limhi himself immediately knew that Ammon and his brethren were not the priests of Noah when they were first brought before him, or whether the realization of that fact came to him because of their story that they were sent from the land of Zarahemla. According to the chronology in Appendix A, about 18 years had elapsed since the death of King Noah and the flight of his priests. [Alan C. Miner, Personal Notes]