So the things that are covered by copyright in software are the creative choices... like, the overall structure of the code, the specific classes, and interface

So the things that are covered by copyright in software are the creative choices... like, the overall structure of the code, the specific classes, and interfaces, etc. Like, there's a zillion ways to organize code (certainly some better than others!) and this is where clean-room design comes into play. It is really unlikely that in a decent sized codebase that the classes, or types, or whatever are going to be substantially similar.