Seeking further clarification as to argument validity

The answer explanation provided for question 26 states that this argument is valid. How is this so? The stimulus states, "In testing our product, Roach Ender, which contains vexone, we have conducted many well-documented studies that prove this fact." It doesn't state that RE only contains vexone. How do we know that RE doesn't contain other ingredients that controls all the other 4000+ species of cockroaches infecting North America? Wouldn't the possibility of other non-vexone ingredients within RE weaken or invalid the letter writer's argument? Thank you!