From the very first verse of the Holy Qur’an was revealed to the last verse (in a period of around 23 years), literally thousands of Muslims had memorised the Qur’an by heart during the time of the Prophet (peace and blessings of Allah Almighty be upon him)… in that same period many Muslims were sent abroad to spread the Message of Islam with only the memory of the Qur’an in their heart.
(Also during the early days of Islam, every time a Masjid was built, it also had a hospital and a school with it which produced further thousands of Hafiz-ul-Qur’an).
Isn’t it a great Blessing from Allah Almighty that to this day (14 centuries later) we still have only one chain of the Holy Qur’an being recited by Muslims in all the different regions of the world?