Perry Como plays a singer Eddie Anders throughout the movie but at the end, during the memorial service for Hart, he is introduced as Perry Como when he comes on to sing the final song at the tribute.
After an opening chorus "Oooo's" and "Ahhh's" to the music of the song, "Lover," Tom Drake says, "You have just heard some words and music written by Rodgers and Hart," even though we have heard no words.
At the Hollywood party at Hart's home, he and Judy are singing a duet. Her dress is cinched with a belt in that scene, however, when she sings a solo just after that, the dress is beltless and her waist is a bit wider. Her hair is also longer than the previous scene.
During the "Mountain Greenery" song a dancer drops a platter which breaks and scatters food all over the stage. A few seconds later the platter and the food are gone.
During the first stage show, Mickey Rooney is shown at the back of the audience clapping. There are a few audience members shown near him. During the second stage show, he is again shown in the same place with the exact same audience members around him as he claps.
The party at which Lorenz Hart meets Peggy Lorgan McNeil takes place during the 1920s, yet the women at the party all are wearing dresses and hairstyles from the 1940s.
After he is rejected by Joyce Harmon, Richard Rodgers attends a showing of Camille (1936). This event is shown as taking place prior to the Broadway premiere of _A Connecticut Yankee_, even though the film was released in 1936 and the premiere of _A Connecticut Yankee_ took place in 1927. The clip from Camille (1936) is shown as if the picture were a silent film, when in fact "Camille" was (and is) one of Greta Garbo's most celebrated talking pictures.
A 26-year-old Judy Garland plays herself set in a scene in which she would have really been around 10 years old. A similar thing happens with the 31-year-old Lena Horne: she would have been about 12 or 13 years old.
When Judy is singing "Johnny One Note," and gets to the line "... and hear the drum," it is obvious that the snare drummer is not playing what we are hearing.