How do you know monks didn't change the story in the middle ages?

This is an ungrounded objection because: These over zealous monks would have had to track down all of the 6000 manuscripts that existed across three continents, in four languages. They would have had to have perfect forgery penmanship in Greek, Latin, Syriac, and Coptic. The codecs of scripture were highly revered and guarded as priceless treasures, so not getting caught doing this would be quite impressive.
They then would have to learn to lie in all those languages in order to fool the audience. They would then need to have all those who noticed the changed silenced. This is a ridiculous conspiracy theory when you consider that these thousands of surviving manuscripts are near identical. As far as conspiracy theories go, this one is an extravagant one. The much more elegant explanation is that those manuscripts are unaltered.