If the Korans are not exactly the same, then I wonder which Koran, if any, was the one angel Gabriel dictated to Muhammad and Muhammad recited to his scribes.
Richard Kroes explains:
Arabic is a 'defective' script: only consonants can be written with it, vowels are omitted. Furthermore, when the Qur'an was codified a script was used in which several consonants shared the same signs. Only 17 signs were used to write 28 consonants. Just 7 signs in this alphabet, called rasm, are unequivocal. About a century after the first compilation of the Qur'an the various consonants were distinguished by adding 'diacritical dots'. From that moment on the five consonants for example that were written with a 'hook' ﺒ b, ﺘ t, ﺜ th, ﻨ n en ﻴ y could be distinguished. Eventually, three centuries later, after some experimenting with systems for the notation of vowels, the vowels were also added.
In 1923 the al-Azhar university in Egypt issued a standard text that is now used worldwide. This standardisation too had its reasons because despite Uthman's standardisation, several versions of the text of the Qur'an developed.
Discussions between traditional Muslims and western scholars of Islam on this topic can run high. On the side of the faithful it is claimed that these only represent the various Arabic dialects or modes of recitation, the qira'at. All 7 (or 10, or 14) are considered canonical. On the side of scholarship however, differences at the level of meaning are recognised.
A good example are the last three words of Q 2:10. In the Egyptian standard edition these are: بِمَا كَانُو ا يَكْذِبُونَ bima kanu yakdhibuna, 'for their persistent lying'. The standard text is based on the text of imam Asim († 744 AD) as transmitted by imam Hafs († 796 AD). It is used in the whole Islamic world, except in North Africa. Here the text of imam Nafi († 785 AD) as transmitted by imam Warsh († 812 AD) is used. In the latter, the same passage runs like this: بِمَا كَانُو ا يُكَذِّبُونَ bima kanu yukadhdhibuna, 'for what they denied'. 'Lying' or 'denying', there is a subtle difference...
for their persistent lying vs for what they denied
So, did angel Gabriel say to Muhammad 'for their persistent lying' or 'for what they denied'? Ignoring the 'subtle difference', these two "canonical" Korans are not identical. Word-for-word, Allah's various books have passages which do not literally match each other. How are Muslims to believe the message in the Koran if Allah cannot keep his word that the written Koran will never be altered?