Continuity mistake: When Nanny discovers the puppies are stolen the calendar in the house shows December. However, the newspaper showing the headline of them being stolen is dated the 2nd November.
Other mistake: When they are counting the puppies at the end they count the puppies on the stairs. One of the puppies has a red collar, only the original 15 have collars, so this dog is counted twice. So the title of the movie should be 100 dalmatians.