The tracker searches for commonly used phrases used to identify anonymous sources so misses anonymously sourced articles that do not use those phrases.
Some matches are false and the article is not anonymously sourced.
Some articles are duplicates because they appeared on multiple news sites. These are typically from wire services.
Some articles are duplicates because they have different urls but come from the same news site.
Some articles refer to anonymous sources but are not themselves anonymously sourced.
Articles that do not have a publication date in Google search results or the URL are not included.
The tracker does not distinguish between good use and misuse of anonymous sources.