In Threepenny Opera, originally (Berlin 2928), "Pirate Jenny" and "Barbara Song" were both sung by Polly Peachum in the first act. In New York in the 50s both songs were moved to later in the play, "Barbara Song" was Lucy Brown's number and "Pirate Jenny" was sung by Jenny.
This left a gaping hole in the Act I wedding scene that has been filled in various ways, none of them satisfactory.
Also the in Second Finale ("Denn wovon lebt der Mensch?") Macheath is sometimes paired with Mrs. Peachum, sometimes Jenny.
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