When the Qumran find was made, they found multiple copies of Isaiah, and the date for the documents is generally accepted to be in the 1st to 2nd century B.C. - a hundred or more years before Christ. Once this was determined, liberals (I'm sure there are still some stalwart holdouts, I just don't know of any) quickly abandoned the argument.
This is just one example, and a doozy, of how the "higher critics", and textual criticism, have repeatedly been shown to be full of crap when it comes to the Bible. There are example after example, throughout the last 200 or so years (certainly since the Tubingen school), where the critics were "sure" something in the Bible was an anomaly that "proved" it was written later than it was supposed, was not historically accurate, was not a "term" that someone knew during a given time period, etc, etc, etc, only to later be proven to be wrong, and the Bible right.
The book of Acts immediately comes to mind. Acts was attacked over and over and over (and still is), and critics were "certain" that Luke was wrong, mistaken, invented things, a liar, there were later additions, that the book wasn't written by Luke, etc, etc, etc - only to later have archeology prove them wrong.
The most interesting stuff, these days, is the stuff going on with Daniel. All of the assertions by critics, about the dating of Daniel (to the time of Antiochus Epiphanes), are being roundly smacked down by some excellent scholars.