The reason for panel layout not listed fully is that the condition for self.indicators_available = True is not satisfied in mate-tweak. The only items listed, 'GNOME2' and 'OpenSUSE' have test not self.indicators_available set which is satisfied.
Installing indicator-datetime (if you had removed it like me to fix panel clock issue discussed in post 29 above) and indicator-session will get back the full panel list.
