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)
Visible crew/equipment: Lightning equipment is reflected in Norma Desmond's glasses when she is drying Gillis by the pool. (00:55:30)