Purina Puppy Chow is one of the worst foods out there, IMO.
My first dog was raised on Purina Puppy Chow, because I didn't know any better, and there weren't a whole lot of choices back then. I always wondered why she had soft stools. At about 5 months of age I switched her to Purina Dog Chow. The vet scolded me for this, so I put her back on Puppy Chow until she was about 9 months old.
As I got older and wiser and had more money, and my dog got older, she started getting better and better food and eventually raw and home-cooked.
She was fit as a fiddle all her life, and lived to be 16 years old.
I've heard stories about dogs and cats living into obscene old age on stuff like Pedigree, Friskies, Purina Dog Chow, etc., so there's clearly a lot about pet nutrition we still don't know.