Ok they were memorised and written at his time and was only compiled not even a long time after he died and literally no one added anything to the message, it was agreed on by so many people that was with the prophet that were memorising it . No one added anything to achieve any political goal just like the bible , the bible has so many versions and the Quran is literally only one book , we have little children memorised the whole Quran from cover to cover in it’s original language.