I get that, what I’m saying is there are bigger narrative and thematic implications for that detail in Luke’s story than simply “setting up the origin of the KoR”, whether those students were the KoR or not isn’t really relevant for the story of this movie, but the ambiguity, the moral greyness and the mistery of what happened are. Luke saying “Ben killed everyone” removes that and also hurts Ben/Kylo’s character as a result. You removed Anakin killing children from LoE to help his character, but here the opposite is done by making Luke’s interpretation of events, that Kylo “slaughtered” everyone, seem like the only possible interpretation of what happened.