As i know if you mod or change some parts of code you have to put this, where do you take a base script and take final credits to you, because if your new compilations has troubbles or something, you have to give support for that and make no responsabilities to the core files, because your work may damage the contents or something, if you code is more secure, even you may have credits to this, because is your work xD. But you have to tell the copyrights and your new licence, but taken the copyleft permission or something like that i don't know how really works this.
But you only add in core files you own code, so you have entire info because you have the entire source code, but you don't ask for support if you change this as you wish xD.
Maybe i'm wrong, but i thing you have all info inside the files, so you can to add your own distro, like linux does.
Only take the credits for the core, but so many authors can make their own distro beause the license tal about this. I thing MyBB works similar to this xD.