These inner lower seals were supposed to be a Cougar only thing, an added measure of sound isolation. Mustangs and Cougars of the 1967 - 73 era share many components including the door shells so the holes were stamped during manufacture. If your Mustang or Shelby has that seal it's a factory mistake. Many Cougars don't have them, it's my guess that this seal was discontinued mid year on the Cougar as being unnecessary.