Muslims believe the Quran to be verbally revealed through angel Jibrīl (Gabriel) from God to Muhammad gradually over a period of approximately 23 years beginning on 22 December 609 CE,[8] when Muhammad was 40, and concluding in 632 CE, the year of his death. According to Wikipedia. I have copied from another site as i do not have the knowledge required to explain it like that.

Anyway in the diagram you can see that they mix gradually, not suddenly as zone of partition is not a fine line. What i am trying to point out is how could a man know this hundreds of years ago? It is obviously not luck.