In the Broadway to Hollywood (1933) sequence, narrator Mickey Rooney states, "I was ten years old when I first came to Metro-Goldwyn-Mayer, and I was raring to go." If he was born in 1920, he would actually have been 13 when he filmed 'Broadway to Hollywood'. This is confirmed by Rooney's admission, later in the film, that he was "a seasoned veteran of seventeen" when he first worked with Judy Garland in 1937.
During her narrative section, Liza Minnelli erroneously states that her mother, Judy Garland "once told me that MGM seemed obsessed with Shirley Temple. They even offered Fox Clark Gable and Jean Harlow just to obtain Temple for a picture Metro was preparing. But the deal fell through, so MGM went head with the picture and cast Momma in the role of Dorothy in The Wizard of Oz (1939)." In fact, Jean Harlow died before MGM began preparations for The Wizard of Oz.
At the beginning of the film, Frank Sinatra says The Hollywood Revue of 1929 (1929) is the "first all-talking, all-singing, all-dancing movie ever made,". In fact it wasn't, the first was The Broadway Melody (1929), which was released in February, nine months before "The Hollywood Revue" was ever released.
In the "A Pretty Girl is Like a Melody" sequence from The Great Ziegfeld (1936), narrator Frank Sinatra says that Dennis Morgan is singing the song. In fact, Morgan's singing is dubbed by Allan Jones, not because Morgan's well-known tenor voice was unacceptable but because Jones had already pre-recorded the mammoth sequence. At the time, the still unknown Morgan was billed by his real name, Stanley Morner.
In the "Melody of Spring" sequence from Cynthia (1947), narrator Elizabeth Taylor self-deprecatingly remarks that she "was certainly no threat to Judy Garland or Jane Powell." In fact, Taylor's singing was dubbed in the film, a point emphasized when she turns up ten minutes later in 'That's Entertainment!' with an entirely different voice in the "It's a Most Unusual Day" sequence from A Date with Judy (1948). In this case, narrator Peter Lawford claims, "That isn't Elizabeth's voice you're hearing. MGM kept her too busy to rehearse and record."