I've had an underutilized hard drive for a long time, so I finally bit the bullet and decided to use diskpart to extend C: by 40GB. Microsoft 's documentation states, "You cannot extend the current system or boot partitions." but of course I know better. 
It seems to have worked properly, but Disk Management did not reduce the unallocated Free space by 40GB as it should have. So according to its math, my drive grew from 160GB to 200GB.
Will this correct itself after reboot, or should I start preparing for the eventual reformat/reinstall?
Actually, looking at Disk Management now, after deleting unused filesystems, I did not delete the enclosing extended partition that is now overreported in size. So I wonder how hosed my partition table is with this "fuzzy math".
DISKPART> extend size=40000
DiskPart successfully extended the volume.
It seems to have worked properly, but Disk Management did not reduce the unallocated Free space by 40GB as it should have. So according to its math, my drive grew from 160GB to 200GB.
Will this correct itself after reboot, or should I start preparing for the eventual reformat/reinstall?
Actually, looking at Disk Management now, after deleting unused filesystems, I did not delete the enclosing extended partition that is now overreported in size. So I wonder how hosed my partition table is with this "fuzzy math".