The NRL accepts one copy of each book (monograph) - the term ‘copy’ referring to publications with no dissimilarities. If two books (monographs) differ from each other with regard to their publisher, illustrator, translator, ISBN number, or in any other way, they are regarded as different copies.
With regard to serials, the NRL accepts only items issued in uninterrupted succession (e.g. 1-10 or 105-116).
The NRL accepts only full annual volumes of periodicals (with the exception of volumes lacking but a few numbers). Also, single issues of serials and periodicals are accepted if reported missing in the Vaari-database.