How Much Established History Do We Really Have About Islam?
First thing is Trust in God. If one trust in God and his book Quran, then he agrees that our Prophet ( PBUH) is messenger of God and he only followed God’s will. Much of later history is widely accepted by majority so what other means one should look for accuracies? History other than Islam as same rule which is what accepted by majority.
How is tawatur related to established history?
Established history only tells us what you have stated in your original question that there was in fact a person in history who claimed prophethood, and other well-known facts about his dawah as well as it’s results. In establishing sunnah through ijma and tawatur, we don’t need to refer to established history of Prophet Muhammad SAW more than that. Please refer to my previous discussions with you in this regard. To establish a sunnah today, we look around at the practice of Muslims and trace it back in order to find any corruptions or innovations.