After a string of courtroom losses in copyright litigation over pre-1972 musical recordings, Sirius XM Radio Inc. hoped a fresh sound and a new front man would give it a hit. Instead, the new release bombed.

This fall, as a federal court in New York found that Sirius had infringed copyrights held by the two founding members of the 1960s rock band The Turtles, the satellite radio company fired its law firms and brought in O’Melveny & Myers. The O’Melveny team launched a new offensive based on a 74-year-old ruling that it said was directly on point—even though its predecessors never mentioned it in their briefs.