In addition to the two examples mentioned below, the original Broadway production lost some chorus numbers explaining the period each scene was set in, and Frank and Beth lost an optimistic duet, "Honey."
When he revised the show in 1985, Sondheim cut Frank's first solo, "Rich and Happy," and replaced it with an ensemble number called "That Frank," whose melody is actually based on the older Cut Song "Honey."
The revision (and most productions that have followed) also dropped the opening chorus, "The Hills of Tomorrow," which Frank supposedly composed in high school, whose melody becomes the source material for all the other songs we hear Frank compose.
Orphaned Reference: The score retains several references to songs that were cut before opening. A fragment of Gussie's cut solo, "Darling," is quoted in the scene leading up to "Good Thing Going," and in "Opening Doors" Frank tells a terrible auditioner "thank you for coming," which is the title of the song that was replaced by "Bobby and Jackie and Jack."
James Weissenbach was originally cast as Frank, but when they determined the show wasn't working with him, they recast Jim Walton, who was playing Jerome, in the role.
Blake Jenner was originally cast as Franklin in the movie version, but left in 2019 after "Our Time" was filmed after a domestic abuse scandal involving him and his ex-wife Melissa Benoist. The song was reshot with Paul Mescal, who assumed the role going forward.
Troubled Production: The original 1981 production was legendary in this respect, partly due to director/producer Hal Prince's decision to forego an out-of-town tryout and hold tryouts in New York, where negative gossip was especially intense. During the tryout period, the lead actor and choreographer were replaced, and the book and staging were heavily revised as the creators struggled to make the audience understand both the backwards storytelling and the Framing Device of having high school students act out the story. By the time they officially opened, Prince made the much-mocked decision to have the actors wear T-shirts with their characters' names or roles on them to help the audience keep track of who they were supposed to be. The reviews were scathing (though Sondheim's record producer went ahead with a cast recording, correctly assuming his songs would be Vindicated by History) and the show's failure ended the Prince/Sondheim partnership.
