The Norwegian band The 3rd and the Mortal are widely regarded as the first band who played metal (doom metal, in their case) with clear female vocals, inspiring many similar bands such as The Gathering and Theatre of Tragedy. Other female-fronted metal bands, such as Warlock, existed much earlier, but to my knowledge they all played heavy metal with shouted vocals.
Is it true that there was no other band, of any metal subgenre, who used clear vocals before 1994?
By clean vocals, I mean a singing style close to classical singing without any edge.