How many original air dates were there for the episode with production code 212?
CREATE TABLE "table1_23937219_3" (
  "series_num" real,
  "season_num" real,
  "title" text,
  "directed_by" text,
  "written_by" text,
  "original_air_date" text,
  "prod_code" real
);
SELECT COUNT("original_air_date") FROM "table1_23937219_3" WHERE "prod_code"=212;