I'm also sceptical as to the professed value of this unpublished material - if it's never been published, no one's had the opportunity to assess whether any of it's any good or not!

There's no problem getting access to the manuscripts to read them, and many people have - they just can't publish them. Given Clare's chaotic life, nobody selected stuff for publication in the usual way. And the newer editions show how much more there was than anybody knew about from the older ones.