Erik Balling wanted the scenes with the cello cases to be accompanied with a cello concerto by Mozart - with the only problem for film composer Bent Fabricius-Bjerre that Mozart had never written a cello concerto. So Fabricius-Bjerre composed one in the style of Mozart on his own; and according to his own statement, it worked so well that several experts in classical music later asked him where he had found that extraordinary piece of music, or even wanted to know its number in the Köchel catalogue.
Near the beginning of the movie, when Egon is released from prison, Kjeld can be seen with a pram. Throughout the entire Olsen Gang series, this is the last sign ever of Kjeld and Yvonne having more than one child. They had three children in the first film (their eldest son, Birger, is never mentioned again ever after); and after this early scene here in the second film, it is always implied that Børge is their only child.