[buzer]

I don't know if they have required old commiters to sign it. I commited to one library that is now under Hashicorp back in 2015 and did not need to sign anything but it was MIT licensed back then. They have also rewritten affected lines as part of larger rewrite.

[Macha]

If it's MIT licensed then they don't need your consent as long as they include the text of the MIT license while your contributions are included.

It's stuff in the MPL period that is more questionable if they don't have contributor sign off.