Other mistake: When they are in San Francisco, notice the pianist. The keys he presses don't correspond with the notes he's supposedly playing. It's a little bit obvious that the music was recorded in advance.
Other mistake: When Dill and Frankie are reading the newspaper, the date on it is 16th November. When they attend the radio show at Earl's Court, the start date of the show on the billboard is the 28th of August. The duration of this film isn't that long.
Other mistake: When Stupor Duck looks into the mirror and sees that the shoulder pads on his costume are positioned incorrectly, look at the mirror and you can see that the "S" on his costume is the right way round - it should be back to front.