"It is the opinion of the authentication board that said work is NOT the work of Andy Warhol, but that said work was signed, dedicated, and dated by him." So reads a 2003 letter from the Warhol Authentication Board, referring to a red Warhol self-portrait from 1965 owned by Anthony d’Offay, which is part of a series of works that have generated controversy and brought one class-action lawsuit against the board.

In a recent article in the New York Review of Books, art critic Richard Dorment details the latest developments in the current struggle over the authenticity of works produced by the famed pop artist, picking up a story that Judd Tully reported on earlier this year.

“Since the Renaissance, a signature is the way artists such as Mantegna and Titian acknowledge[d] the authenticity of their work,” Dorment writes, noting that the work in question is not only signed by the artist but actually inscribed to Zurich-based art dealer Bruno Bischofberger with the following note: “To Bruno B Andy Warhol 1969.”

The Authentication Board, though, says a signature and inscription are not enough. Because Warhol’s onetime assistant and manager Paul Morrissey has said that Warhol was not present for the fabrication of the works in the series — Warhol gave the printer detailed instructions over the phone, he said in a 2002 interview — the Authentication Board says the works cannot be genuine.

Warhol is said to have loved the self-portraits, lobbying Sam Green, curator of Warhol’s 1965 retrospective at the Philadelphia Institute of Contemporary Art, to include them in the show. The paintings even grace the cover of scholar Rainer Crone’s 1970 catalogue raisonné of the artist’s work, a copy of which Warhol signed for d’Offay in 1986.

In 2008, d’Offay sold his art collection to England for £28 million ($46 million), which Tate Director Sir Nicholas Serota referred to as “the greatest gift this country has ever received from a private individual.” The collection was believed to be worth about £125 million ($203 million). Dorment notes that one work from the donation still remains with d’Offay: the signed, red self-portrait, which currently has no legally acknowledged creator.

Read more at the New York Review of Books.