 What date did season 12 premiere? 
CREATE TABLE "table1_2655016_4" (
  "season_num" real,
  "series_num" real,
  "episode_title" text,
  "original_air_date" text,
  "nick_prod_num" real
);
SELECT "original_air_date" FROM "table1_2655016_4" WHERE "season_num"=12;