Like most arguments of this type it assumes the conclusion then acts like it’s terms don’t do that.

If Mary knows everything about red then she also knows what seeing it is like. If she doesn’t… then she doesn’t. They try to have it both ways by hand waving & hiding behind colloquial language but it still comes down to that in the end.

The thought experiment just reveals the writers own biases & limitations of thought rather than be revelatory in any way.

In fact this paper is often used by opponents of qualia as demonstrating why they are nonsensical & incoherent.

Got to say, I agree. Daniel Dennett has his flaws but his argument that this type of thought experiment is a category error & that qualia do not exist and are incompatible with what are basic facts we know about neuroscience should have ended this years ago.