To remove the original copyright notice, they'd need a copyright assignment (possibly implicit, as when the work is made for hire). They've already got a licence and they've infringed it by doing this.
Well they could technically have proper attribution without the literal string "Copyright (c) 2024 The Spegel Authors" if they included an older copyright notice that was more appropriate. I think that was the point they were making.
This is correct and is roughly what I meant. My only nitpick is that I was thinking that if they forked at the time of the older notice, they would be fine to have used it, rather than a vague notion of appropriateness that probably was intended to mean the same thing, but is less precise.
The hacker news post reached someone high enough up at Microsoft to have things changed. They ended placing a combined copyright notice that is a mixture of both versions into the repository to play it safe.
