Hmm does that including legendaries too? Or you just happen to miss buying one, I know I almost did. But thank god I caught on before it is too late, Fashionista and Master of Arms is probably the easiest gold medal to unlock.
Yes, you definitely miss buying one by accident, next time, be extra careful and go from top to bottom again, just to be sure. Or you can look up how many costumes for each class and then go and count how many you have for each class, then you will know if you missed one.