What you're saying doesn't make any sense. If what you're saying was true you could take any MIT repro, fork it and replace the license with a fully proprietary copyright claim or any other license. You absolutely can't take code and just change the license to anything more permissive without the original copyright holders permission.
It's definitely the case that at a given snapshot of the repository which has copyrighted code owned by someone else the copyright notice has to be there at that same revision.
It's definitely the case that at a given snapshot of the repository which has copyrighted code owned by someone else the copyright notice has to be there at that same revision.