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.
Purge is a series of connected one-shot comic issues set as a follow-up to Revenge of the Sith. A handful of Jedi who survived Order 66 unite to do something, once and for all, about the evil Galactic Empire and the Emperor's dark enforcer. Vader isn't upset that the Jedi want to resurface, because he has a singular focus—to track down Obi-Wan Kenobi.
Darth Vader brings death to the Jedi who survived Order 66. His legend grows as he roots out Jedi, crushing their lives, their hopes, and all memory of their kind from the civilizations that now bow to the Galactic Empire.