i believe your understanding is basically correct
although papa nelson says emphatically in his past writings that the class a to class ab transition is not a finger trigger noticeable transition, it is in fact very subtle in practice once music is playing... almost imperceptible (otoh clipping is VERY noticeable)
his view is that the key in great amp design is to have fairly high class a bias to keep the first few watts delivered very pure and low in distortion - so i think the idea of having the bias meter move occasionally on musical crescendos is quite alright