escape yourself and gravity

So I've been thinking a lot about Severus and his service to the Dark Lord, his time in the Death Eaters, why he got out, that sort of thing.  I've received a lot of praise for his story in "Ashes and Possibility", but since my newest fic-in-progress is not Severus/Ginny, I want a new backstory.  So while working that out, I've come up with a couple of questions.


1. Lord Voldemort.  He started going by that name early, and yet in the books we only ever see the Death Eaters and Severus calling him "the Dark Lord" or other various honourifics.  Why is that?  My impression was that people called him "You-Know-Who" out of fear of his name, sort of a lupus in fabula that if they name him he will appear.  Is that the same reason the Death Eaters do?  Or did they call him Lord Voldemort before Harry defeated him the first time?  The Lexicon claims that Severus 'refers to Voldemort respectfully as "Dark Lord"*--but is it respectful?  I wonder.

2. When did Severus leave the Death Eaters?  HBP would have us think that it was when the Prophecy was made in 1980 (the Lexicon says 1979--is that for sure when the Prophecy was made?).  I don't have my book on hand, so I can't check this just now.  The Lexicon also says the following: that before in 1981 but before October, he 'Approaches Dumbledore and offers to be secret agent for The Order of the Phoenix'*'.  So at some point between hearing the Prophecy (and was it 1979 or 1980? this is important!) and October of 1981, Severus realized whom Voldemort was targeting, and was suddenly penitent?


* Lexicon quotes taken from the Lexicon's Snape page.