In the beginning, a black car rolls into the garage where Guy works, and Guy is asked to assist with the car's problems. This car is actually Roland Cassard's and it can be seen two more times: when Roland visits the umbrella shop to give Ms. Emery the money for her pearl necklace, and again as the wedding car. The license plate is the same and can be seen in this latter scene and in the very first.
At the ending scene, Geneviève mentioned about picking up her daughter from Anjou. In reality Anjou is 4.5 hours drive away from Paris, and from Paris to Cherbourg is 3.5 hours in an opposite direction. That makes this "detour" a very long drive.
The children in the final scene have personal connections to the filmmakers: Genevieve's daughter Françoise is played by Jacques Demy's adopted daughter by Agnes Varda, Rosalie Varda-Demy; and Guy's son François is played by composer Michel Legrand's son.