Little Bird was added into "Everyone Makes Mistakes" via recycling illustrations from "Big Bird and Little Bird's Big & Little Book" (which was also drawn by A. Delaney), with a running gag involving Little Bird attempting to make Big Bird tell the truth. This was most likely done to help pad out the story to an extended length to fit the running time for video length.
Some names have been changed on this video. Susan is renamed "Mrs. Washington" and voiced by Fran Brill, and Slimey is renamed "Squiggly" and is voiced by someone other than Martin P. Robinson.