The New Shadow and Melkor

[Lord of Angmar]

As many of you know, Tolkien began writing a sequel to the Lord of the Rings called The New Shadow, only to discontinue his work on it. Upon reading it over (and for the record I am glad that he did not finish and the story was left as it was) I noticed a very strange occurence.

Borlas, an elderly man of Gondor, is talking to his young friend Saelon, in the opening (and basically the only) scene in the attempted sequel. In this scene, Borlas talks about Melkor and the first Darkness:

The evils of the world were not at first in the great Theme, but entered with the discords of Melkor... [Men] entered afterwards, as a new thing direct from Eru, the One...

First of all, Tolkien states clearly in several works that Melkor's name was never uttered in Middle Earth after the First Age, and that if anyone ever did refer to him, he was 'The First Dark Lord', the 'Dark Power' or , on occassion, Morgoth. But never Melkor. Do you think this was a Tolkien mistake in the writing, having a mortal man (and not a very learned one at that) speak the name of Melkor, and then go on to talk about Eru and the Themes (which I did not know most if any of the peoples of Middle Earth knew about)?