As far as core / matrix in a generic cortical system, it’s hard because it often kinda conflates with primary / higher order. Thalamic circuits vary a lot connectivity-wise.
Matrix projections generally don’t go to L4, so maybe the point is maybe those thin L4s do receive some thalamus but possibly no core thalamus making it not like normal L4, maybe vestigial or normal synaptic connectivity messiness with no useful thalamic input to those thin L4s.