There are 10 unique codex entries in the Game Rules section on the Imperial Fleet. 1 is accessible to all players regardless of class or faction and 9 are unobtainable.
Advanced Class: Mercenary is unobtainable.
Codex type: Game Rules | Faction: Imperial | Class: Bounty Hunter
Associated Achievement: None
Advanced Class: Operative is unobtainable.
Codex type: Game Rules | Faction: Imperial | Class: Imperial Agent
Associated Achievement: None
Advanced Class: Powertech is unobtainable.
Codex type: Game Rules | Faction: Imperial | Class: Bounty Hunter
Associated Achievement: None
Advanced Class: Sith Assassin is unobtainable.
Codex type: Game Rules | Faction: Imperial | Class: Sith Inquisitor
Associated Achievement: None
Advanced Class: Sith Juggernaut is unobtainable.
Codex type: Game Rules | Faction: Imperial | Class: Sith Warrior
Associated Achievement: None
Advanced Class: Sith Marauder is unobtainable.
Codex type: Game Rules | Faction: Imperial | Class: Sith Warrior
Associated Achievement: None
Advanced Class: Sith Sorcerer is unobtainable.
Codex type: Game Rules | Faction: Imperial | Class: Sith Inquisitor
Associated Achievement: None
Advanced Class: Sniper is unobtainable.
Codex type: Game Rules | Faction: Imperial | Class: Imperial Agent
Associated Achievement: None
Galactic Strongholds is obtained from interacting with a Clickable Plaque.
Codex type: Game Rules | Faction: Both | Class: All
Associated Achievement: None
Social Points is unobtainable.
Codex type: Game Rules | Faction: Both | Class: All
Associated Achievement: None