Windows 7 / Windows Server 2008 R2 Service Pack 1 Revision Issue
A revision was made to the WSUS offering for Windows 7 / Window Server 2008 R2 Service Pack 1 (SP1) on 5/24 to address known installation issues. We are aware that this latest revision is incorrectly reporting as "Not Installed" for machines that have already installed the previous revision of the SP1 update.
Windows 7 / Windows Server 2008 R2 Service Pack 1 Revision Issue - WSUS Product Team Blog - Site Home - TechNet Blogs