Audio problem: When Peter is hinting to Carol that he is still growing, the audio changes to being dubbed in from Peter separate from the actual scene after Peter stands up and mentions he wants cowboy boots. Then the audio is back to normal once Peter mentions "Brown" cowboy boots.
My Sister, Benedict Arnold - S3-E5
Continuity mistake: When Kathy Lawrence enters the Brady home, as she walks through the kitchen, her top button is unbuttoned. When she is in the living room cheering, it is buttoned.
The Not-So-Rose-Colored Glasses - S3-E13
Continuity mistake: In the middle of the episode, a boxy gold station wagon is pulling into the Brady driveway, which immediately cuts to a shot of a rounder body style, gold station wagon pulling up to the carport.
Revealing mistake: When Carol goes to the dress rehearsal, she is wearing one outfit when she is talking to Mrs. Goodwyn, but then when she goes upstairs to the girl's bedroom and talks to Marcia, she is wearing a totally different outfit.
Suggested correction: Carol was talking with Ms. Goodwin during school hours, and when talking with Marcia about it in the bedroom, it was presumably evening. It's possible Carol may have taken a shower in between that time frame offscreen, thus changing her clothes.
Dough Re Mi - S3-E16
Plot hole: Greg bought a time spot in the music studio to record a song. He writes a sudden new song for the studio at the last minute and then, next scene, the kids are singing the song in the studio along with background music playing. Where did all the instruments come from and who was playing them? Even if pre-recorded, Greg and the other kids would have just shown up at the studio at their time, and no way they would have been able to get the tracks down in advance to an unknown song like that.
Continuity mistake: At home, before leaving for the Grand Canyon, the trailer was much taller than the car, and looked more like a motor home. After that, it becomes a different vehicle more like a trailer, about the same height as the car. When the prosecutor steals the car, it's the tall version, and when they arrive at the Grand Canyon to look at the view, there's nothing attached to the car bumper. When they leave the Grand Canyon it's the shorter version, back to being a trailer.
The Power of the Press - S3-E19
Continuity mistake: The book in Jan's arms keeps moving; first the front is facing outward, then the back, then the front again. (00:13:40)
Factual error: About 1/3 through the show, Greg has to talk to Marcia and asks Peter to leave. On the way out Peter stops to start recording on the tape recorder. He only pushes the play button. He would have had to push the red record and play button to record their conversation.
The Power of the Press - S3-E19
Continuity mistake: The book Peter's classmate is holding rotates between shots. (00:10:00)
The Big Bet - S3-E18
Revealing mistake: When Bobby closes the sliding door behind him, the curtains swing outward and through where glass should be, revealing it to be an empty frame. (00:01:15)
Continuity mistake: When Greg runs into the girls' bedroom to rescue Bobby from the window ledge, there's a black stuffed animal sitting in the middle of the bed nearest the door. After Greg pulls Bobby into the room, the stuffed animal is at the head of the bed. (00:03:45)
Continuity mistake: The football diagram that Greg draws on the chalkboard changes from shot to shot. (00:07:00)