It's my understanding that the Dead Sea Scrolls line up fairly well with other copies of the same works, where other copies exist. The differences are about what you would expect given the different times they were put to paper (absent special precautions, errors tend to creep into texts and a fairly well understood rate - you can compare two hand-copied texts to get some idea of how closely they are "related" given that they came from a common ancestor copy).

Also, from their discover in the mid-20th-century until the 1990s, the content of the Dead Sea Scrolls was available only to credentialed scholars. In the '90s a researcher published a very complete
"index," indicating every occurrence of every word by where in the scrolls it occurred. The index was so complete it allowed other scholars to reconstruct the original. At that point, the scholarship monopoly was broken.