Definitely seems someone needs to try and research his record, especially before the Rooke fight. I found a report of that fight, and it mentions a few fights.
The Sportsman - Wednesday 13 March 1878
Concerning the valiant Denny himse lf not many particulars were forthcoming. He is vaguely accredited with having figured in a "whole heap" of fights with varying success. Many of his "scraps," however, have apparently been off-hand affairs, and are scarcely worthy of mention. He is known to have fought and vanquished Jemmy Price, and to have bestowed a similar favour on Harry Holden. Then he encountered Charley Davis, and a hot battle was the result, the matter ending in a furious dispute. Eventually, however, the cup for which the men contended was awarded to Davis. Harrington has also had a go at Jem Goode, and the hostilities extended over 1hour 25min. On another occason Denny was matched with Calden, of Wapping, whom he defeated. His friends last night proudly claimed for him that title upon which the veterans of the ring appear to set so much store, namely, that of being unbought and undefeated. In a glove contest with Bat Mullins, however, it is recorded that he had to give way.
If anyone has any more info on him, I'd greatly appreciate it. The fight itself was a pretty scrappy rough affair. With both hammering each other early, and Rooke resorting to biting Harrington, before being KOed.