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Best practice in the past has been to catalog nonfiction comics under their subject heading
If a graphic nonfiction title is about the 9-11 Report, catalog it under HV6432.7 for Terrorism -- Specific country -- United States -- Specific incidents -- September 11 Terrorist Attacks 2001. If a nonfiction comic is a biography of the jazz musician, Charlie Parker, catalog under ML419.P4
Fiction graphic novels and comics are often cataloged under their country of origin, not by author last name. For example:
PN6765-6768 for graphic novels by Italian authors
PN6725-6728 for American authors