The Traveling Library
Each formatted citation in your Word document is saved with field codes that embed reference data in the document. The paper contains a "Traveling Library" of references cited. See Field Codes in Microsoft Word.
The first time a citation is formatted, EndNote looks in the open library and finds the corresponding reference. If you later reformat, EndNote again looks in the open library for that reference. However, if the library is not available or not open, EndNote uses the Traveling Library for reference information.
Because reference data is kept with each formatted citation, you can collaborate with other authors on a paper without each author having the same EndNote library.
The reference data saved with each citation includes all fields except Notes, Research Notes, Abstract, Figure, and Caption.
Note: Do not unformat your document if you do not have the original references in your libraries. Unlike formatted citations, unformatted citations require that you have the corresponding EndNote libraries open in order to format references.