Many boxers who've been stunned won't admit to it. Or, because they were stunned, they don't remember it. Rocky had his bells rung and saw stars at least once, count on it. He was human.
Other fighters tend to be self deprecating and exaggerate, claiming they were hurt worse than they really were.
I can relate to that Joe DeAngelis story. As an amateur I had a hard punch but I ran into a couple of guys who simply refused to acknowledge that I could KO 'em. No respect at all for how hard I was hitting.