Continuity mistake: When you see Mason sitting in his corner and he leans over to look at Rocky and then you see Rocky's calf flex. Dixon is not wearing boxing gloves, he only has tape on his hands.
Continuity mistake: When Rocky is outside of Marie's place convincing her to visit the restaurant, her necklace keeps disappearing and reappearing between shots.
Continuity mistake: After the final fight Rocky is walking to the dressing room and waving to the fans. He then stops and hugs Spider, then Marie and her son and then Duke and they walk off. The camera then goes back into the ring where they announce Dixon has won. But in the bottom left of the screen you can see Duke still in the ring but he had already left and had gone back into the dressing room.
Answer: Stallone himself answered this question in an interview. "When Rocky was diagnosed with brain damage he never went for a second opinion and yielded to his wife's wishes to stop. So with the advent of new research techniques into brain damage, Rocky was found to be normal among fighters and he was suffering the results of a severe concussion. By today's standards Rocky Balboa would be given a clean bill of health for fighters.