I thought I had seen it but it turned out it was Allentown Joe Gans against Tiger Flowers with Bill Tate as referee and Harry Greb was one of the judges. True story.
You are mistaken. The fight you saw was Allentown Joe Gans against Bill Tate with Harry Greb refereeing, Tiger Flowers signing the national anthem and Dakota Montana (the Arizona Kid) judging at ringside. This is a common mistake as the cannister was mislabeled when they translated it from cyrillic. You can tell because Gans-Flowers took place at noon, and it's clear from the shadows in the ring that this fight took place around 12:25 p.m. I had it authenticated by the next-door neighbor of Nat Fleischer's great-grandnephew, who spent a summer working as an airbrush artist on the Boardwalk in Atlantic City.
Rumor has it that Boston Tom McMustache and Chocolate Negro Kid boxed an exhibition on the undercard.
Again, urban legend gets it wrong ... it was Young Chocolate Negro Kid vs. Non-Pariel Boston Tom. The timeline of all four boxers' careers confirms this.