There are several good copyright sites on the Web. My impression is that if the words are "virtually identical", then Dylan had no legal right to use them without permission or to claim that they were his, and I believe he also had no right to change them without permission. However, you never know. He may have just copyrighted his additional verse and the music (if it's his), and the album may say "music and additional words by Bob Dylan", in which case this would just be a mistake by the people who run the lyrics site. Or various other possibilities.