Continuity mistake: As Cinderella descends the staircase after her wedding to The Prince, she is obviously wearing a long sleeved gown. When she waves through the window of the carriage, however, the gown is short sleeved.
Other mistake: When the clock strikes 8 o clock, the 11 (XI) on the clock reads 12 (XII) in roman numerals. This is just in-between the scene with the mice making Cinderella's ball dress and the scene where the carriage arrives at the home to pick the stepmother and stepsisters up for the ball. (00:36:50)
Continuity mistake: After throwing the bookends away, the King leans on the table and stares at the Duke. In the first shot the King's tummy lies on the table and his left hand grabs the left edge. A shot later he is half a meter away, standing by the table with both hands lying by his belly.
Continuity mistake: The Fairy Godmother turns the four mice into horses. When they change back three of the mice are the same, but one is different. It goes from Jaq, Gus, Luke (the little mouse in mint green) and one of the twin mice to Jaq, Gus, and both of the twins. Luke is absent.
Continuity mistake: When the king throws his crown and breaks the window, note the lower part, a part shaped like a V is standing out. In the shot following it's now shaped like a lower case R.
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 ★