The “Harvard style” is not an actual style, it is not associated with Harvard University - see their statement. There is no official manual for the "Harvard style" but it has historically been associated with the author-date style. There are many variants which follow the author-date convention, including the American Psychological Association (APA) and the Chicago Manual of Style.
The "UQ Harvard" guide is based on the 6th edition of the Style manual for authors, editors and printers, 6th edition (Snooks & Co. 2002)
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Note: This guide was updated on April 15, 2021