Please, what panels have improved and how do you know that?
Panels constantly improve - yoiu yourself have said that many times. Even the same technology from panel to panel varies in how well it was implemented. I had a look at some S-IPS TV's the other day and the contrast ratio really does make for a washed out image. Even in the pics above I see that of the stone building.
Anyway to answer your question - panels even within the same models improve, i.e. A01, A02, etc. So there is no need to ask how we know