Professor James A. Bellamy writes:
These variants, however – I have counted more than two-hundred that make a difference in the meaning - are important in that they tell us there was no solid oral tradition stemming directly from the prophet to prove which variant was correct.
In Surah 6:63, of the seven readers, the two from Kufah recite ‘njyn‘ (anjana) “he saves us.” and the other five ‘njytn’ (anjay- tana) “you (sg.) save us.” These two words sound so dif- ferent that no one, unless he were deaf, could mistake one for the other, and the words on both sides of the word in question are unambiguous. One cannot argue that the prophet used one variant one day and the other the next. Nor can one maintain that there is a firm oral tradition that guarantees the reading of the unambiguous words but breaks down when more than one reading is possible.
Reference: James A. Bellamy (2001), ‘Textual Criticism of the Koran’. Journal of the American Oriental Society. Vol. 121 No. 1 (Jan-Mar. 2001), pp. 1-6.