I'm aware that this topic may have come up many times before but I couldn't stop myself from asking.
At a basic level, when we consider the many variant readings of the quran we naturally infer that, while they may be equally valid, not all of them can be correct. Even a small grammatical difference can result in widely dissimilar interpretations. It would also be ludicrous to assume that the quran was revealed to the Holy Prophet in tens of different ways.
For example, yara vs tara in 2:165. Both cannot be correct; at least one has to be false; there's no other way around it. But does this not then validate tahreef? From this doesn't tahreef become a historical fact?