One could argue that Co-Authored by Copilot means 'not under copyright'

The headline literally says the line is being inserted regardless of usage, which makes it easy to argue that it’s entirely meaningless as an indicator of AI use at all.

Yeah the current guidance from US copyright office is that if it were said to be solely authored by copilot it would not be eligible for copyright. If it were said to be solely authored by human A (who happened to use co-pilot) the elements and arrangement of it not generated by co-pilot would be copyrightable. I’m not sure the copyright office has released guidance on attempting to register AI as a co-author I assume the registration would be rejected but you’d be able to re-submit as sole Human author.