Y already have SP1 but since that update its several months, sure I have installed more than 8 updates since SP1.
Have you checked both links in the WU panel to see if the update count agrees: "Installed Updates" and "View Update History". I show total of 32 under Windows. This is a new problem for me; never experience this before ... That I know of anyway. But problems do pop up from time to time so I'm not surprised.
+1 Time to start checking the system if all else fails. As to KB2534510, I see it in the link's website but the Microsoft Download Center shows nothing and I don't have it on my "legit" Windows 7 system. KB971033 is available and KB2534510 may be its counterpart for XP, 2000 or some other OS. But definitely just guessing on that.