Several threads on this forum are about transferring publications from one library to another (e.g. group to personal, or other way around), but I could not find any description of what happens to (linked) citations in documents. For references that do not move, Zotero allows you to update the bibliography etc. If for example a title has changed, or an author is added in the Zotero app, and you press the update button in Word, the bibliography will be updated. Importantly, if you add the same citations in the same Word document again, and then select it not from the 'cited' list but from the same library as the original reference in Word, it will not add a duplicate item in the bibliography, but recognizes that the already cited item was selected again and refer to the same item in the bibliography.

All this does not work when items are stored in two different libraries. When citing an item and selecting it from e.g. your personal library and then citing it again and selecting it from a group library, a duplicated will be added in the bibliography. This is understandable, though perhaps not desirable, as there are two copies. However, suppose that you have created a document using references stored in a group library. Later, you decide to move everything to your personal library (dragging and dropping and then removing the items from the group library). If you then open the document and add one of the originally cited items again, but select them from the new collection in your personal library, it will create a duplicate in the bibliography. Also, if an item is updated in the library (e.g. the author list), the refresh function in Word will not recognize it.

Is there any way to prevent this loss of link from happening? If not at this time, would it be an idea to generate some unique identifier that can be used to track the same items along libraries. For example, it may be possible to use some kind of hash that may be based on the DOI or ISBN, along with some other aspects (perhaps the same aspects that are also used for recognizing duplicates and allow merging them in Zotero)? Such an unique identifier may also be used to link items in different libraries, so that updating that item in one library (e.g. personal) also can be used to update the same item in other libraries (e.g. a group library).