The film featured 55 "spot removal artists". In order to make the dalmatian without spots, "Oddball", completely white, the production team tried putting make-up on the dogs, trying to paint off the spots, putting plain white suits on the dogs, finding another breed of dog, none of this worked so eventually the spots had to be removed digitally, erased in each shot.
The movie that the dogs are watching when Chloe and Kevin go out for a date is Lady and the Tramp (1955). The specific scene is when Lady and Tramp go to Tony's Italian Restaurante. The restaurant that Chloe and Kevin go to on their date is named Tony's Italian Restaurante.
Many of the puppies found happy homes with many of the trainers. Most were returned to the breeders once they were too old to use for filming, and the breeders sold them off with special papers, noting that the puppy took a part in the filming of this movie.
Cruella's license plate changes subtly between this movie and 101 Dalmatians. Here it is DEV IL; in the previous movie, it was DE VIL. DEV 1L is a legitimate registration number in the UK and many owners of these "cherished" number plates (illegally) re-space the characters to make them better spell words. Perhaps Cruella was caught.
When Cruella arrives at Le Pelt's factory, she enquires if the workers are illegal immigrants. Le Pelt nods and says "50 Francs a week". Cruella says that isn't much and Le Pelt replies "That's all I can afford!" This is a variation on Woody Allen's lines in "What's New Pussycat", when he is talking about his job in a strip club, where he helps the girls dress and undress.
The trivia item below may give away important plot points.
In the beginning of the movie we "meet" Doctor Pavlov in the prison Cruella is. He is obviously named after the Russian physiologist Ivan Pavlov who is renowned for his landmark study on conditioning, using dogs as test subjects. In Pavlov's experiments, a dog was taught to expect a morsel of food whenever it heard a bell ring, hence the joke that Cruella's "cure" is reversed when she hears the bell toll of Big Ben.