BBY/ABY is used to position items along the Star Wars Timeline. BBY refers to Before the Battle of Yavin. ABY refers to After the Battle of Yavin. The Battle of Yavin in Episode IV: A New Hope occured in 0 BBY/ABY.
The Youtini Expanded Universe Ranking system is a 1-5 scale that ranks EU book quality, difficulty, and importance. Books closer to Level 1 are easier to read and understand, more important, and of higher quality.
Getting cut in half by Obi-Wan Kenobi and being rejected by his former Sithmaster Darth Sidious isn't going to defeat Darth Maul. In fact, it only makes him mad enough to take on the galaxy, with an army of Mandalorians!