Not only that, but clean room implementations aren't a requirement. Functionality isn't copyrightable. Even when a copyrighted codebase is changed piece by pi

Not only that, but clean room implementations aren't a requirement. Functionality isn't copyrightable. Even when a copyrighted codebase is changed piece by piece, there's case law that expressly invalidates the Ship of Theseus License the article links to: https://en.wikipedia.org/wiki/UNIX_System_Laboratories,_Inc._v._Berkeley_Software_Design,_Inc https://en.wikipedia.org/wiki/UNIX_System_Laboratories,_Inc.....