I've been an aficionado all my life and caped a few calves in Puebla and Tlaxcala in the '70's. I know that Arruza and Procuna performed in Nogales and I even saw and met El Cordobes there, but the great Juan Belmonte? That's a little hard for me to believe. I can't imagine never having heard about it. Jr. perhaps? If there's any truth to it can whoever wrote it on your website provide any documentation?
Belmonte was brought in in around 1914 or so in a wooden bullring placed there for a special corrida in a portable ring. He was on the card with gaona. Gaona ended up killing the bulls as Belmonte suffered a huge goring. It is accounted for in the books by Dick Frontain.