The ones who failed it have definitely felt an RNC in the past. I can't see any of them getting in MMA fights and not having an RNC on them in the past-and I've seen videos of at least one of them where they are put in an RNC in the video.Those who won probably know what a RNC feels like. They probably have a good sense of what it feels like before it sets in. Those who don't know what it feels like probably didn't know what was going on until it set in.
But by that point they are tired. They've essentially just gone through 3 rounds in a row, with their senses heightened before each round and some anxiety. They're not going to react immediately, and likely weren't expecting it after getting pushed/shoved to start the earlier rounds. Some people take longer to react, and that's why practicing no-minds is useful rather than just practicing 'normally' all the time.