The Plath materials, in Series 3, "consists of materials relating to Sylvia Plath including writings (poetry and prose) by Plath, writings by others about Plath, printed material by and about Plath including reviews of her works, materials relating to books published after Plath's death, and information regarding the Plath holdings at Smith College and Indiana University."
"Any material relating to Sylvia Plath that was found on the verso of another item elsewhere in the collection was photocopied and added to this series, with a note on the bottom as to where the original item is located in the collection."
The Plath materials are organized in the following way: Poems, Prose, Posthumous books, printed materials, writings by others; holdings in other repositories, and other material. Other material is my favorite way to classify the hodge-podge that inevitably enters an archive with any set of papers.
Several years ago I requested photocopies of some of the materials in the collection, and found the archivist I dealt with to be friendly and efficient. It was in part due to interactions with her that I am now studying to be an archivist. The entire collection is worthy of review if you find yourself in the Atlanta area.
The finding aid to the Ted Hughes papers is online here. The Plath materials are in Series 3. The picture above is taken from here.