So I have a theory.
I BELIEVE: All pokemon spawns near you are static and do not change (In my case I have found out where all 2 paw print pokemon spawn for me if I am in my house, I walk down 1 house and turn the corner and they always appear there.) I have tested this a good 20+ times now so it has to hold some weight. Have yet to bother to hunt down a 3 paw.