macsforme I can also confirm that one of my 2015 machines has a harsh panel while another has a calm panel (subjectively). The other two have not been tested extensively yet.
macsforme Three of the four (including the one I subjectively find most comfortable) return the exact same entire EDID string, while the fourth is not a byte-for-byte match but when parsed by edid-decode all values still appear to be the same.
Just in case anyone might rely on it, I wanted to officially recant my claim that one of my four 2015 15-inch Retina MacBook Pro screens was more comfortable than the others. In fact, all four seem uncomfortable in roughly equal degree. There were some differences depending on the operating system version and configuration running on the machine each screen was connected to, which initially led me to mistakenly believe there was a variation. At the end of the day, after a day or two of use (with a delayed onset), all of these 2015 15-inch Retina MacBook Pro screens give me headaches and vision problems.
I plan to make another thread sharing more research and overall findings regarding this MacBook model with regards to eye strain.