Import already existing references
When you import a RDF files from an other zotero database that contains the same ref than yours then you get them twice in your library.
Could be nice import only the ref that you don't have.
Could be nice import only the ref that you don't have.
Dan Cohen said "We're definitely going to have duplicate detection in a (near) future release. There are, however, some complexities to doing this right--e.g., if there are minor variations in the metadata for two books that are really one book, which one is canonical? Anyway, we'll work this out and have some options for handling duplicates well (or deleting them)."
See this thread: Duplicate Detection