Factual error: In the scene where Cinderella is in her new room at the Prince's castle, the roses prominently displayed in the foreground are brightly coloured Hybrid Tea roses (the pointy ones) which were not bred until the early 20th Century. In the 1700s (panniered skirts and powdered hair) the roses would have been of looser formation, with softer colours, e.g pink or cream cabbage roses. (These roses also appear in later scenes.)
Continuity mistake: When Cinderella is running away after losing her slipper, she lifts her skirt, and she is wearing only stockings. In the next scene when she is singing a reprise of "He Danced With Me", she starts dancing, and she is wearing her normal shoes.
Answer: It's the same slipper, after failing to find Cinderella, the Prince erects that monument to his lost love.