Elastic promises "open"—delivers proprietary

Err... derivative works are definitely not limited to files you edit. If you have a program A and you edit a dozen files and then release it again, the *whole work* is a derivative of the original, even though most of the files were not edited. (Similarly, if you edit a book and change half the chapters and then republish it, the new book is a derivative of the old even though half the chapters are unchanged.)