"Little Sadie" is a traditional folksong, and as such would be in the Public Domain. Bob Dylan's copyright would extend only to any substantially new material (music, arrangement, lyrics) he added. Please remember that the US Copyright Office does not issue copyrights. A composer owns a copyright by virtue of authorship. What the US Copyright Office does is register claims. Anyone can attempt to claim anything, but not all claims can be successfully defended in face of challenges.

--- Steve