Some Questions About the High Elf Quests

I have some questions about the storyline while doing the High Elf introduction quests.

1. Wasn't the Witch-king called the Witch-king only after the founding of Angmar? Why is he already referred to as the Witch-king during the Battle of the Last Alliance in the game?

2. Why does the Witch-king call Sauron "Sauron the Great"? I remember that "Sauron" is a Quenya word — it's a derogatory term used to insult him. Who would refer to themselves by that name, or address their own master that way?