*Warning possible spoilers*

While I was finally doing Vol I Book 15 a few days ago, there was a certain instance where you actually meet Sauron under his elven disguise during the second age amongst the Mirdain.

But lo and behold, while I was clearly expecting Annatar The Lord of Gifts as clearly documented in The Silmarillion and The Unfinished Tales (or Lost Tales? Can't remember or find the books again in all my boxes) and now he is renamed Anathron.

I'm wondering why the sudden break with the lore when throughout, the game has been fairly thourough in sticking with Tolkien's works.

Does anyone have an explanation?

Regards