Hilda Aguirre did not sing her songs but was dubbed by then unknown Estela Nuñez. For years, this was kept a secret, Nuñez never had her name in the credits. It was Enrique Guzman, years later, in an interview, who revealed the truth.
In Spain all the actors were dubbed to the Spanish accent. Only the songs were saved in the original Mexican accent.
The character performed by Enrique Guzmán was named like him in the Mexican accent version, while in the Spanish version he was named Ernesto Nieva.