Plot hole: Ashley says she is 9; later in that season, in "Just Infatuation," Phil says she is almost 12. Will is 17 for the first two seasons, and 18 in season three. Nicky Banks grows from baby to preschooler between seasons four and five (though this was humorously addressed).
Character mistake: When Geoffrey serves tea after his sassy cough at Vivian's sentence about High Tea not being a sacred institution, the actor messes up when it's time to actually serve tea, with a napkin getting caught in the teacup saucer. Granted, accidents do happen, but it's quite uncharacteristic for the perfect butler Geoffrey is portrayed to be, and simply a flub by Joseph Marcell. (00:17:45)