Deliberate mistake: In the famous sequence where the pumpkin turns into a carriage, the fairy godmother stands behind it waving her wand and doing the magic. First mistake: After the transformation, the fairy godmother is stuck in freeze frame with her hands up in the air for the entire time when Cinderella is saying how lovely the carriage is. Another mistake occurs when it cuts to the fairy godmother (after the freeze frame), because her arms are suddenly down and she is moving and talking to Cinderella.
Deliberate mistake: The first time we see the King, the bookends and books are sketchy drawings that bear no relation to the fully detailed ones that we see afterwards.
Answer: Cinderella's entire outfit was magically created by the Fairy Godmother. Not only was the spare shoe Cinderella had in her possession identical to the other one, it likely would be charmed so that she is the only one who can wear it. It's similar to young Arthur being the only person who could pull Excalibur from the stone because he was the true king. No other woman who attended the ball wore glass slippers. If they had, they'd be able to also produce the spare shoe as proof.
raywest ★