From 2003 - 2005 there was a Mars database available to certain Keyhole subscribers. This disappeared about the time that Keyhole became Google Earth. Between 2005 and February 2009, no Google provided planetary imagery existed. But several Google Earth Community members did provide views of Mars as overlays. Some of these overlays, although useful at the time have longitude shifts compared to true Mars latitude and longitude.
Then in February the new high resolution database with higher resolution layers and correct latitude and longitude rectification was introduced with GE 5.
Placemarks posted prior to February 2009 may or may not still be relevant. Those that are not will be merged to a new post heading under Mars which should help to avoid confusion about placemarks which no longer show at the correct location.
Go to Mars Archives to see posts which may have useful content, but which are not displayed properly with the GE 5 Mars.