Visible crew/equipment: When Albert and his friends are in front of Doris' house they are singing a song about going to the park. As they are finishing the song and leaving to go to the park, you can see the reflection of the microphone in the window of Doris' house.
Continuity mistake: When Doris is watching The Fat Albert Show, she is holding the remote out just above her knee. When her tear falls down, it falls directly in the middle of the remote.
Continuity mistake: When Bill Cosby (appearing as himself) opens his door to find Fat Albert there, Fat Albert puts his hand out to shake Cosby's. In the next shot, he puts his hand out again.
Continuity mistake: At the track meet, Laurie runs the third leg of the 4x100 and hands off to Doris to run the anchor leg. At the finish line, Laurie is there to cheer on Doris as she crosses line first. Only the first and second runners of this relay would have time to make it to the finish line in time to see the end of the race.
Deliberate mistake: Old Weird Harold's pants fall down twice in the film. His boxers are different colors each time; once they're red, the other time they're blue. The director admits to this deliberate mistake in the commentary, siting his interest in seeing if people will notice.
Continuity mistake: In the live action shots, Fat Albert always has a belt. In almost all of the cartoon shots, he doesn't have a belt, though he does in a few cartoon shots. The director admits to this mistake in the commentary, though he apparently only noticed it in one shot.
Other mistake: When Fat Albert and the Cosby kids are in the classroom with Doris, it shows two girls at their desk laughing at Fat Albert. The girls have keyboards, but no monitors.
Factual error: When Fat Albert and Reggie are racing around the school track, there are palm trees visible over Fat Albert's right shoulder in the background. The problem with that is the movie supposedly takes place in Philadelphia, PA.
Deliberate mistake: Fading is mentioned throughout the film. However, according to the director in the commentary, they don't really start to fade until the third time it's mentioned.
Visible crew/equipment: When Doris is sitting on the steps at the party, Fat Albert walks up and tries to convince her to dance. In one of the shots, the boom mike is casting a shadow to Doris' left.
Audio problem: There are several times in the scene at the party where Fat Albert supposedly says "Hey hey hey" but his mouth is closed.
Answer: He has said in many interviews that they were based on his friends growing up. The characters of Bill and his little brother Russell, were Bill Cosby and his brother Russell. Thou the adventures were exaggerated, the characterizations were real.