REMINDER!!
Most parts of the Qur'an was written during Muhammad's (pbuh) time. Not all of it perhaps. But the important thing is that there were people called khafez (meaning save, keep, protect) who memorized the whole of the revealation under Muhammad's instruction. Even today khafez institution is strong and there are millions of khafez who can write Qur'an again without any mistake in a word.
Qur'an was recorded during Omar's and Othman's time because, due to the wars, number of khafezes were decreasing. The written pieces were proof-read by many and many khafezes.
I know many people who can read all 600 pages of Qur'an out of their memory. Khafezes are very blessed because they are the key to the authenticity of the Qur'an. If there are khafezes around no one can dare to make a change in Qur'an.
God save them inshallah.
Unite