I suggest that even if the two of them altered every text they could find they couldn't possibly find enough texts out of possibly hundreds of copies to change future copy content forever. I liken that to splitting a down pillow on a windy day on a hilltop. You probably would not have all your pillow back. Someone finding just one feather could rightly suspect there might still be a nice pillow to be had. Copies of the texts, at least portions of the whole, were by their day widely distributed, the finding of one unaltered copy exposing forgeries compared to it. I suspect many texts resided in many synagogues and in some private hands.
Taking all of the texts together yields an amazing amount of agreement, probably most differences being simply missing chapters or whole books. I expect Jesus read from a Hebraic scroll, not the Septuagint, inside a synagogue. The Septuagint was apparently meant for Jews living in areas where Koine Greek dominated, which Paul doubtless mastered along with Aramaic, as needed in his travels. Hebrew was honored as official for Jews in His time and location, with high assurance all official scrolls were authentic copies of the most ancient available text. One slight error would have been easily detected resulting in burning of the whole document. Dead Sea Scroll studies are revealing much about the times of Jesus.
