Bro the order of verses in the Quran is simplay based on how the Prophet (sa) used to recite the Quran.
And surely he would sometimes recite the whole Quran in one sitting. And in Ramadan in Taravih prayers as well he used to recite the entire Quran
The Quran was not only written down but also memorized by many Muslism in the life time of the Prophet Mohammed (sa)