The flashback of Liliane and Antoine arguing is, in fact, a clip from A Noite Americana (1973), in which both also played lovers despite the film not being part of Antoine Doinel saga.
François Truffaut later admitted that he was fully aware he was making a big mistake while shooting this film.
The title of Antoine Doinel's book, he portrayed by Jean-Pierre Léaud, is "Les Salades de L'amour". In A Noite Americana (1973), a character summarizes Léaud's character's love life as, "les salades de l'amour", and another follows up with, "That would make a good title of a book."
While being asked by an interviewer what movie maker she would like to work with if she went into film business, Dorothée instantly answered François Truffaut. As this came to his knowledge, Truffaut then asked her to work on his next Antoine Doinel feature.
Actress Dani, who plays Antoine's lover Lilianne, also appeared in François Truffaut's A Noite Americana (1973). Much like this movie, she, in that movie, is also named Lilianne, and also plays the lover to the character portrayed by Jean-Pierre Léaud. Lilianne's speech to Christine about why she is breaking up with Antoine is verbatim to what Lilianne says to Jacqueline Bisset's character, Julie Baker, about breaking it off with Léaud's character in Day for Night.