Deliberate mistake: Right after Betty tells the joke about the owl and the bungee cord, it shows everyone laughing and Betty is standing, but when he says "Enough." he stands up again. (00:25:10)
Deliberate mistake: When Betty is about to fight Master Tang he is holding the chain, but when the music starts he doesn't have it. (00:31:40)
Deliberate mistake: When Chosen One is dancing in front of Betty, take a look at Betty's face. There is a moment in which the face of the double playing Betty is visible.
Deliberate mistake: At the beginning, when The Chosen One is a baby and is rolling down the hillside, he loses a booty. In the next scene, he is wearing it again. He has them for the rest of the movie.
Answer: Some scenes/shots were taken from the old movie, while others were made specifically for this movie. Additionally, numerous shots were "composited" to place new characters in the old footage.