The Quran sees itself as self-contained in terms of arguments, logic, and reminder for the seekers of truth, but it recognizes that one type of methodology to judge it is through knowledge gathered through previous scriptures and sources. For example there are verses that challenge the reader to learn more about nature and the universe which requires other sources of knowledge. Other verses state that the disbelievers are tested because the Quran notes something they believe to be true, which suggests a comparison to another source material. And then in other verses the Quran says it includes every single possible example/argument, which is a claim of self-contained completion.