Papers taken over by the Opies from other collectors and researchers they were friends with.

Roland Knaster (?1892-1979) was a book and ephemera collector. Peter Opie first met him in the mid-1940s. After his death the Opies acquired a number of children's books and ephemera from Knaster's collection, and also took over some of his working papers, such as collection lists, bibliographical references, correspondence and articles, as well as auction catalogues (now with MSS. Opie 293-314) and memorabilia.

Charles Morris was the Oxford University Press representative in Glasgow, who had an interest in children's book illustrations, and also collected children's books. After Morris died in c.1973, Peter Opie helped his widow with selling the book collection, and the Opies also acquired some of the books, notably 20th century material, for their own collection.