You don't understand my point (probably my mistake).
If the file starts with:
// <MIT header>
// Copyright evantbyrne
Then a fork should read:
// <MIT header>
// Copyright evantbyrne
// Copyright Microsoft
But if you did not add "// Copyright evantbyrne", the MIT license doesn't say that Microsoft should add it. I don't even know if it's legal for Microsoft to do it. You have to add your own copyright to the files where you own a copyright.
If the file starts with:
// <MIT header>
// Copyright evantbyrne
Then a fork should read:
// <MIT header>
// Copyright evantbyrne
// Copyright Microsoft
But if you did not add "// Copyright evantbyrne", the MIT license doesn't say that Microsoft should add it. I don't even know if it's legal for Microsoft to do it. You have to add your own copyright to the files where you own a copyright.