Revealing mistake: "Railway Station" (Adventure 2, Part 3): Steel orders Tulley to light all of the abandoned station's lamps with matches. But after the lamps are lit, they give off a steady illumination and don't flicker. It's obvious that they all have electric bulbs in them.
Revealing mistake: "The Creature's Revenge" (Adventure 3, Part 2): This apartment building has unbelievably clean elevator cables. Steel takes off his coat and then ties a knot in the cable - without getting a single grease smudge on his hands or his pristine white shirt.