When it comes to Elidibus and his memory loss I had always thought whatever said promise was and to whom it was made to must have been either not important enough for him to remember or that it was tangled up with a bad memory. As he tells Emet Selch that he doesn't want to look at the memory crystals because why remember something if you're just going to forget about it all over again. Now I wonder if said promise might have conflicted with the rejoinings or with his role as a primal that only remembered their function.