The claim: "The Qur'an has different readings (qirāʾāt) and codices; so the text may have changed / been corrupted."
The Qur'an's own claim
- "It is We who sent down the Reminder, and We will surely preserve it." (15:9)
- "Falsehood cannot come to it from before it or behind it." (41:42)
- It is "in a preserved tablet (al-Lawḥ al-Maḥfūẓ)." (85:21-22)
A variant reading ≠ a different Qur'an
The qirāʾāt are mostly small differences at the level of vowelling / pronunciation over the same consonantal skeleton (the Uthmanic rasm); they are not separate / contradictory Qur'ans. There is no difference that overturns the meaning; so the variant readings do not break the integrity of the message.
An honest limit
Fact: historical-critical scholarship studies and debates early manuscripts, the Uthmanic standardisation, and the qirāʾāt literature; we do not pretend that is "closed." But the inference "a variant reading = textual corruption" is not automatically true: these differences are limited and documented, and do not show "a hidden tampering." While debate continues over the scope and nature of the preservation, the claim "the Qur'an changed beyond recognition" is not supported by the available evidence.
Source: Qur'anic verses (M. Okuyan meal). Presented soberly and respectfully, with a text/interpretation distinction.