You won't see the difference right away if you go on the surface or in an other area. What I mean by that is, if you kill the rats in the sewers and go to the surface right after, the rat population haven't changed yet. You have to give it some time. (At least, that's how I think it is, I do not have that much experience with that system yet.)
I also had a quick lock at the Rats stuff and everything looks fine to me, both in the toolset and from my experience IG lately. You probably are just unlucky or maybe the rats really loves you!