(I admit I could be projecting my lack of understanding; I’m not rock-solid on the experimental setup yet.)
Still to me, it matters if the linearity been described can be observed directly _in_ the model. My understanding is that it is not; rather, it is tested with an additional model. The term probing can be misunderstood; it isn’t -just- an internal probe. There are ‘derivative’ models as well.
This raises questions about what we mean when we we are talking about internal representations! In my view, a derivative of an internal representation is not the same thing.
(I welcome people who can educate, correct me, or even reframe the topics. The above thoughts are subject to change.)