Does that mean that all those projects using CLAs may end up at some point with someone saying "I want you to remove the part of your codebase for which I have

Does that mean that all those projects using CLAs may end up at some point with someone saying "I want you to remove the part of your codebase for which I have a copyright"? I mean in practice nobody will ever be able to do that, just like most licences are just completely ignored. But I mean in theory?