[Lukongsimi]

The Quran means recitation. When the Quran was revealed, it was immediately recited and memorized.

From day 1, we know who the memorizers were. We have their names, their background, their families, etc.

Till today, the Quran is still recited and memorized all over the world.

If someone says that the Quran has not been changed, whether they be Muslim or Non-Muslim, they have just proven that they don't know anything about the various Qurans existing today.
The oldest Qurans available today are the the Samarqand codex (currently located in Russia) and the other is an old Qur'an manuscript kept on public display in the Topkapi Museum in Istanbul.
Both are incomplete manuscripts. Without a complete copy from Uthman's period, it is impossible to know that the Qurans used today (which aren't even in Qurashi Arabic, the original dialect use in Uthman's version) are the same.