When was the film released that a less than 5038 production number and was of the character Bosko?
CREATE TABLE "1931" (
  "title" text,
  "series" text,
  "characters" text,
  "production_num" real,
  "release_date" text
);
SELECT "release_date" FROM "1931" WHERE "production_num"<5038 AND "characters"='bosko';