[Pitchwife]

Not to forget that in the first draft for the Council of Elrond, Elendil (aka Valandil/Orendil) was referred to as a Numenórean king ruling lands that had formerly been part of Beleriand; so obviously at this time Beleriand was conceived as not quite so completely sunken as it later turned out to be.

As for the Nogrod/Khazad-dûm/Longbeards question, the Etymologies, as far as I can see, don't offer any other possible meaning for Enfeng/Anfangrim than 'Longbeards'. So at the time Tolkien decided that Nogrod and Belegost were the homes of the Firebeards and Broadbeams, rather than the Longbeards, neither of those houses can have been called Enfeng any more.