All the plaintiffs would need to do is provide evidence that copywritten code was produced verbatim. This includes showing the copyrighted code on GitHub, showing copilot reproducing the code (including how you manipulated copilot to do it), showing that they match, and showing that the setting to turn off reproduction of public code is set.
It makes no difference who owns the copyrighted code, it need only be shown that copilot is violating copyright. Microsoft can't say "uhh that doesn't count" or whatever simply because they own a company that owns a company that owns copyright on the code.
All the plaintiffs would need to do is provide evidence that copywritten code was produced verbatim. This includes showing the copyrighted code on GitHub, showing copilot reproducing the code (including how you manipulated copilot to do it), showing that they match, and showing that the setting to turn off reproduction of public code is set.
It makes no difference who owns the copyrighted code, it need only be shown that copilot is violating copyright. Microsoft can't say "uhh that doesn't count" or whatever simply because they own a company that owns a company that owns copyright on the code.