From what I have ran into about store sizes is every one seems to have different definitions of what is what. That is why I go by weight on ball pythons under 500g. One reptile shop I used to buy from, their mediums looked like larges. The shop I buy from now breeds their own rats but they classify them as pinkie, fuzzy, weaned, small, medium, large, jumbo. So fuzzy to them is anything from your normal idea of a tiny rat with peach fuzz on it all the way up to eyes opening. So I say take anything said with a grain of salt since you are the only one who knows the exact size of your snake and the size of the food. Like I said though, I used to weigh the first one I got to get an idea of what size I needed from that store. Once I got the general idea, then I could just eyeball them. Also helps that they bring the rats out for me to look at. Plus knowing the weight helps a lot if you plan to order frozen from online as they all list the weights of their prey so you know exactly what you need. But once your BP gets over 500g, then you can just go to small rats and keep him/her on that for the rest of their lives.