The day and date of Orville and Zelda's wedding anniversary is only correct if action is happening in September 1961, but the calendar in Polly's trailer is for September 1962.
Near the beginning, Barney (played by Cliff Osmond) is seen running from his gas station to show Orville his new lyrics. But when the shot changes to inside Orville's house, Barney (just visible behind a pillar outside) is now standing stock still for a few seconds, as the actor Osmond waits for his cue to run into the house.
After Orville's wife digs under his sweatshirt for a pen while Johnny is playing the piano, the sound of the piano distorts as if the sound tape slowed down for a second.