Footnotes using identical citations should not use short footnotes and instead use reference names, typically using the <ref name="AuthorYYY"> syntax.
Per
Wikipedia:Citing sources, please continue to maintain the same style of use when adding citations using the
{{sfn}},
{{harvnb}} and <ref> syntax. Footnotes will be altered to fit this article's style if they do not conform to the following rule:
The only cases where short footnotes are allowed is when a source has multiple footnotes to different pages or footnotes to the same source are unique in some other way such as due to quotations or annotations specific to a particular footnote. In these cases the full citation for the source appearing in the References section may be referred to by short footnotes using Template:sfn or similar template to make the footnote to the particular page, or indicate the quotation, annotation or other unique information particular to the footnote. Short footnotes referencing citations in any other section violates this style. See the article for usage examples. If you have any questions or problems, please ask on the talk page and someone will be happy to help you. Thank you.