The Batman Arkham Knight season pass includes all content for the game, including those exclusive to specific retailers.
Following initial confusion, a post on the Warner Bros. Forums has sought to make things clear and explain that retailer content will become available once its period of exclusivity expires.
“Throughout the 6 months of additional Batman: Arkham Knight content, Premium and Season Pass owners will receive all in-game content that is offered through various retail pre-order incentives. This includes the Harley Quinn and Red Hood Story Packs, as well as any Batmobile or Booster Pack that was available as early bonuses for pre-order of the game. For those who did not receive the content with their game, these items will become available when their respective exclusivity windows expire in August/September.
The tl;dr version of this is: Premium Edition & Season Pass owners will receive all retail exclusive DLC after their respective early access periods expire.”
Fans looking to pick up Arkham Knight but unsure about which retailer to go with can at least take solace in the fact that the exclusive content can be enjoyed if you choose to grab the season pass, too.