Heh, i agree with all the arguments BUT! I think It's likely a small oversight designed for a cool reveal. I would place it under the "a wizard did it" folder.
All though his books are so cohesive and well thought out. Maybe ear piercings follow special rules.
In short what I'm saying is: maybe it's a mistake? Maybe not? Thus I just stole 10 seconds of your life to and made no substantial argument. Now that time is mine, mwa ha ha ha