Installation of transition flashing

I am installing a metal roof on my house. This is standard exposed fastener roofing. The house is a standard gable roof, but on one side of the home there is a shed addition. So there is a change in pitch at this point. It goes from a 9/12 to a 5/12. The company that sold ne the roofing sent me what they called "transition flashing" and bent it to the correct angle for this pitch change. These came in 10ft sections. The run across the roof is 32 feet. I called the company an expressed concern that should snow sit in that transition valley, would I be at risk of water running under the seam since this is not a continues piece of metal? They said water should flow down and as long as there was a foot or so overlap, This should not be an issue....Should I believe that????

Not a dead valley, just a transition. I did speak to someone at the company about the installation. I didn't feel confident whoever they gave me to talk to actually was knowledgeable. They didn't suggest a sealant. Maybe I will call back.