Medieval Christian readers noted the Qur’an’s piecemeal revelation and surah divisions

Evidence

Some statements made by the Annotator of Ketton’s text were extraordinarily judicious. He was conscious that the constituent revelations of the Qur’an are separate, and puzzled to know how the whole could be thought to be revealed from a heavenly prototype. He explained that its separate writings (cartae) are called surahs, and that Gabriel is supposed to have brought them from God, not all at once, but bit by bit. ‘For through the whole of this Book no word is ever ascribed save to God conversing with Muhammad’, he pointed out. — Norman Daniel, Islam and the West, 225