MLA

Koch, Frederick R. (Frederick Robinson). Music/Pablo, boléro. Box 329, folder 1841. n.d.. https://collections.library.yale.edu/catalog/12218310.

APA, 6th edition

Koch, Frederick R. (Frederick Robinson). (["Box 329, folder 1841"])(n.d.)[Music/Pablo, boléro]. https://collections.library.yale.edu/catalog/12218310.