A question that comes up on the Open Source board: "is this a mirror?" and "is this a fork?". We exclude mirrors, and the answer is a little more involved than it looks.
Mirrors
A mirror is a copy of a repository, kept up to date automatically, usually by the same people or by a distribution. It has the same issues, the same pull requests and the same discussions, and its star count is a copy of the original's.
We exclude mirrors, and the number of them in the catalogue is currently zero — because a mirror is not something you discover by searching, it is something you follow. It appears in a search because a README links to it, and at that point you can see that the content is identical.
Forks
A fork is a different thing. A fork is a copy somebody made to change. It may have a different direction, a different maintainer, a different licence, and it may be more active than the original. microsoft/autogen and the frameworks that came out of it are the example: the fork is the interesting one.
So forks are kept, and they are listed as what they are.
Renamed repositories
The interesting case. When a project changes its name or moves to an organisation, the old URL redirects to the new one, and GitHub keeps the original's star count and issue history. The redirect is not a copy; it is the same repository at a new address.
If we treated the old address as a separate project, it would be a second row with the same stars, the same issues and the same README, and it would appear in the ranking as if it were independent growth. That is the failure we are guarding against.
The rule we use is that a project is identified by the repository's identity, not by its name. A repository that has been renamed is the same project, with the same number, and the site's link to it follows the rename.
Why the distinction matters for the ranking
The weekly list measures growth. If a renamed repository counted twice, one project's growth would be counted as two projects' growth, and a transferred repository would look like an organic rise. The ranking is only comparable across weeks if each repository contributes exactly one daily point, and the de-duplication is what makes that true.