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And the 2nd answer seems to say that no, you can't just recopyright something. https://law.stackexchange.com/a/4150

Some answers seem to disagree. I, as a non-lawyer, think as long as the git commits make it clear who authored what, it's a non-issue.

See the Software Freedom Law Center's guide:

There are multiple examples of how to recopyright MIT-style source under the GPL.