How did Muslims understand Quran in the life of Prophet and four Caliphs without note books?

How did Muslims understand Quran in the life of Prophet and four Caliphs without the existence of books of Tafsirs, Hadiths, and Contexts? Answer is: they understood Quran only by Quran because Quran fully explains itself, which mean: Quran does its own Tafsir (exegesis) through its own internal built-in Tasreef and its own built-in dictionary. And this is Only the Correct way to understand Quran correctly. Also, logically and rationally; Infallible Book of Infallible God cannot be explained through Fallible Books of Fallible men. In order to write Tafsir of Quran, a Person must have more knowledge than Author of Quran, or at least level of his knowledge/Intellect must be same as of Author of Quran. Now, we all know: Author of Quran is One God. Then, is there any Mofassar (exegesis writer) who have more knowledge than God? No way. In Quran 75:19, God says about Quran that “It is for Us to explain it”. And Quran indeed does its own Tafseer through its own Tasreef 6:114, 25:33, 18:54. This mean: all Quranic verses are interconnected like brain neurons. And in this way, verses explain each other in multifaceted forms. For example: when we read Surah Baqara (Cow) of Quran, we see two terms, Muslim, and Momin. New reader of Quran might pause a while and think; Oh: then what is difference between these two terms? But when reader proceeds further and reaches to Surah Mominoon; he reads there full definition of “Momin,” and in short, it becomes clear that if a Muslim is equated to an Engineer, then a Muslim-Momin is like a Professional Engineer who really practically applies all laws and ethical codes of Book of God in his temp earthy life. Quran explains itself very beautifully.