Shouldn't Canelo been ineligible for the title for missing weight since it is a common rule in boxing?

I know the WBC which is based on Mexico loves him that's why they gave him a title shot. But does he really deserve it. He missed weight and in most fights if you missed weight you are ineligible to win the title even if you win. Lok at Concepcion when he missed weight against Donaire, he was not allowed to win the title even if he wins or Joan Guzman who went overweight over Funeka. Guzman won but he could not get the belt from Funeka because he was ineligible by the IBF for missing weight. But why is Saul Canelo Alvarez an exception?