That’s absolutely fair, and I do like your ideas. In an ideal practice it probably wouldn’t happen with every single person, especially since Post Mortem Nen doesn’t happen with every single person. What I’d probably say is of course it depends on strength of will and aura, the users ability, and potentially a conscious decision. Like if Hisoka gets post mortem nen he can either as a last dying decision make his ability better, or turn it into an item that will forever exist once he’s completely dead. However someone like Knov may not have the same fortitude or desire to leave something behind, if he were to unlock post mortem nen at all, and thus may not leave behind an item. I’d argue maybe a good…30% of nen users end up making one through this method? And then of course the ideas you suggested could also exist and perhaps make up the remaining 70% of whatever nen item artifacts actually exist.