No, it didn't go into limp mode.GM probably already knew there was enough proof out there with the 2015s and 2016s to expose them to some liability. Changing the cooling system for the 2017s was a good idea to limit their liability for another model year. Unfortunately, are you saying that the 2017 Z06 owner that was at VIR with you had overheating issues? You wrote that he complained that his car was running hot, but do you know if it went into limp mode?
Nevertheless, as you said, in 70 degree weather without really pushing the car to its limits, that wasn't a good sign...