Legacy content is the term given to content from an earlier game included among the resources of a later one using the same engine, despite not being used. In many cases this content is clearly not meant for the setting of the latter game, or is an obvious remnant from other, deleted resources. There are two games in the Fallout series that contain legacy content - Fallout 2 (content from Fallout) and Fallout: New Vegas (content from Fallout 3).
Because Fallout: New Vegas legacy content was simply carried over from Fallout 3, most of its core information remains unchanged; things like weight, value, alignment (for non-player characters), and base ID's are unchanged. Behavior may not remain the same, as certain quests or scripts may no longer be present, or the conditions which would make items or content behave in a certain way no longer achievable. Additionally, while many of these resources remain, often the textures associated with them are gone or changed.
Note that legacy content should not be confused with cut content, as the two differ in certain areas. Legacy content consists of the content from an earlier game that has not been modified in any manner (with the exception of certain elements being removed i.e. removed textures, scripts etc.). Cut content can consist of legacy content that has been adjusted for the later game (example:Nuka-Cola Quantum in the base Fallout: New Vegas game).
List of legacy content
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