Forgive me if you already know this. The MSKB says
"The Last Known Good Configuration feature uses information that is saved from the last time you shut down your computer to restore registry settings and drivers. Because of this, you can use this feature only if you were able to start your computer successfully prior to restoring your system by using the last known good configuration.
After you start your computer by using the last known good configuration, changes that were made since the last successful startup are lost."
Therefore by definition, the date of the last good configuration is always going to be the date of the last successful shutdown. Hope I'm not teaching a duck to suck eggs here.