The cite_error_references_duplicate_key error occurs when two ref tags have the same name attribute but differing content. We want to know how prevalent the error is across wikis.
Data to answer this question should already be available in the per-wiki summaries produced by our HTML dump scraper.
Probably not relevant, but I want to mention that we are currently abusing this error message in two other situations when something is wrong with a Cite-Extends. These code paths are obviously not enabled on production wikis.
There are also two slightly different code paths that show the same error message. It's possible there are different user stories behind these two situations.
<ref name=a>x</ref> <ref name=a>y</ref>
<ref name=b>x</ref> <references> <ref name=b>y</ref> </references>