When training a dog, rewards immediately must follow good behavior, and punishments, if you use them in training, immediately must follow bad behavior. Otherwise, you risk the dog associating the reward/punishment with the wrong behavior. If we punish Psy now for something he did in 2002, he might assume wrongly that we only disapprove of Gangnam Style. It's too late to correct his 2002 behavior. We just have to make sure we smack him with a newspaper if he ever starts doing it again.