I might not be able to explain well, but from what I understand about how github works, when you fork someone else's repo, github only stores 1 tree but you have your own set of tags / branches. This led to an issue that was probably fixed where if you set a repo to private, anyone who had a clone could guess commit hashes from their fork's remote. Another interesting thing about git is that you can have 2 root commits (the Linux kernel has 4 root commits iirc).

Because of these 2 "features", when I clone dmca and run `git pull some_ytdl_git_mirror master --allow-unrelated-histories`, I end up with a giant source tree that consists of both repos joined by a merge commit. Because no rebasing happened, no history was changed and it can be pushed without force permissions. Now that all the youtube-dl commits are in the same tree as the dmca repo, you can access them regardless of what fork you've cloned via `git fetch origin <hash>`.

I hope that makes sense?