[no label] is meant to be effectively the same as “self released”, so we won’t be adding a separate entry for that. It’s not meant to be “the label is not printed, but there is one”, it’s meant as “there is no label releasing that, and that is known”. Yes, that does also apply to a few other cases, such as many (but not all) bootlegs, but that shouldn’t be a problem: if a release is “official, [no label]” there’s very little else it could be but a self-released release. I don’t see anything “[self released]” would add over “[no label]” set to “official”, really.
The alternative is to do what Discogs does, and actually have a different label for each artist’s self-released music: https://www.discogs.com/search/?q=Not+On+Label&type=label - personally, I find that to be a horrible mess (and I can’t even imagine how much worse it gets if several artists are collaborating on a self-released release - does it get assigned to all of the artists’ self releases labels? Do we try to find out which of the artists actually took care of the releasing?)