"John Tyson" wrote in
:

The files aren't additive, but they overlap; I think the best bet is
to have both loaded, but make sure the new one is being used if the
HIT is located within it (uncheck the box for the first file).

Are you SURE the files overlap?

Here is the KML outlining updated Steve Fossett search areas in red.
http://www.gearthblog.com/kmfiles/searchforfossett.kmz

Notice the two updated Steve Fossett search areas do NOT overlap.
http://www.flickr.com/photos/13636939@N06/1389992170/