They aren't assuming that, and it's weird that you would claim they are. Where do you get this? Those in the field of textual criticism are well aware of the

They aren't assuming that, and it's weird that you would claim they are. Where do you get this? Those in the field of textual criticism are well aware of the existence of "variant texts"—those "textual witnesses" (documents) that differ for various reasons from the sources they were copied from.