myself on Nostr: No. You can create your own NIPs and implement them in your own client (or relay). ...

No. You can create your own NIPs and implement them in your own client (or relay). "Official" NIPs try to simply "sync" different clients. But clients sometimes do what they want. A good example are reposts. Fiatjaf hates them and there is no NIP for them (there used to be a basic one but it was taken down) but most clients support them.