When using Harvard, you should use the publication date in your reference, not the reprint date.
The reprint is simply when a publisher has initially published a fixed number of books, say 5000 and when they've all been sold they have to 'reprint' some more, which means the content is exactly the same as the original print run.
Cite Them Right has advice on what information to include in your full reference for reprinted and facsimile editions.
Note: This is different to a new edition where the text has been updated. In this case, you must use the date of the edition you are citing.
