A system and methods are disclosed for maintaining a composite history of changes to a program comprising two parallel histories. In accordance with one embodiment, a computer system identifies a first history of changes to a program, and generates a second history of changes to the program based on the first history, where the second history has a final version of the program that is identical to a final version of the program in the first history, and where the second history excludes changes to the program in the first history that introduce an error that is fixed in a subsequent change to the program in the first history, and where the second history includes all other changes to the program in the first history. The computer system then generates a third history of changes to the program that comprises the first history and the second history.