Some properties from them will be used as fallback (composited, hottracking color?) only for compatibility for current skins. All properties must reside in StartPanelComposited::StartPanelPriv, it makes no sense to spill them - other parts were used to behave like Win7, but they're no longer in aero.msstyles. PandaX may just include definition of those parts into Win10 classmaps from Win7.