Responses
I have a theory about this that might not be entirely true but I've been a fan of corpse party for a long time now and I think the reason Naho and Kou are still remembered in the real world is because Sachiko needed Naho's blog to continue bringing people into the school for her. Kou is remembered too because since Naho was just as strong as Sachiko, she wanted the world to remember her sensei and all his work so her soul's desire is the one thing keeping his existence alive.
This is just a theory again but hopefully this helped you :). Sorry if there is any mistakes as well or this doesn't make sense. (≧∀≦)
☆this might contain spoiler☆
What i don't understand in these series is that if you die in tenjin elementary and your existence is whiped out in the reality, how is it possible that kou kibiki and naho are still known in the reality. Logically her site with the charm shouldn't exist at all the moment she died in tenjin, right?
~sorry for any grammar errors or bad language~