Determining which _levels are occupied

Trying to write a function on _level0 that will let me find out if any Flash movies are loaded on _level1, _level2, etc. using loadMovieNum.

for example, in _level0; if I:
loadMovieNum (“movie2.swf”, 2);
loadMovieNum (“movie3.swf”, 3);
function();

… this function would tell me that no SWF has been loaded into _level1 (unoccupied).
(for… in, perhaps?) I tried to use getInstanceAtDepth(N); but returns undefined as I don’t think it works with loadMovieNum.

BACKSTORY: I have several _levels representing pages of content that lay on top of each other. When I loadMovieNum(“movie5.swf”, 5); I don’t want user to be able to click on movie clips (onPress) on _level4, which are hidden behind _level5.

I don’t necessarily want to kill _levels 1 - 4 before loading _level5; want user to be able to close _level5 and go back to _level4, e.g.

I know how to disable/hide on case-by-case basis, but I’m trying to develop and call a global function on _level0 that will look for occupied _levels and disable/hide the appropriate movie clips on each level and cut down on scripting, since not all levels 0 to N will be occupied in every case.