kind off... if you look in thier tool catalog, they advertise having sets by number (1-10) and under each set, it shows you what tools were added on to the set before it. This keeps you from getting duplicates. So, For example, the difference between the 310pc set (1) and the 400 piece set (2) might be a set they call limited access, which features swivel sockets, stubby wrenches and crowsfeet. Kind of hard to explain what I mean, but if you look in thier catalog you will see. IMHO, buying an add on kit is sort of a waste, considering they giv you alot of stuff youll rarely, if not ever use. Just buy the stuff when you need it, or when you think your gunna need it. I agree with red, Alot of times it is cheaper to just buya small set of thier sockets rather than buying them individually... I bought 5 or 6 specific craftsman sockets for the kart, and it wound up being like $21. For that money, I could have gotten the little 3/8 and ratchet set they advertise, but buying individually is always like that.
Jim