Answer: Year of publication and issue number, if there is one.
Step-by-step explanation:
There are quite a number of referencing style conventions available in the world today with some of the most prominent being the APA style, MLA and the Chicago style.
Harvard has its own referencing style that may not be as popular as the above but is very well known nonetheless. When referencing using the Harvard style and the year of publication and issue number needs to be included in a print or e-journal reference, it is to be placed in a round bracket. If there isn't any then there is no need.