determining movie clip positioning on a dynamically created grid

I followed this tutorial to place my movie clips into grid positions. Each movie clip contains a text with their respective numbers. I want to be able to determine which movie clips are on the leftmost and rightmost column using an if statement. I was able to determine the top, bottom, and corner movie clips but I can't figure out how to check for leftmost and rightmost. In this example, movie clips 4 and 7 are leftmost  while 6 and 9 are rightmost but I need a code to determine the leftmost and rightmost even when the number of movie clips in the grid are changed. I hope my explanation is clear enough. I would appreciate any help. Thank you.

Here's the code i have:

var tileCount:int = 12;

var rowCount:int = 4;

var colCount:int = tileCount/rowCount;

var col:int = 0;

var row:int = 0;

var space:Number = 2;

for (var i:int = 0; i < tileCount; i++){

     col = i % colCount;

     row = int(i/colCount);

     var mc:MovieClip = new box();

     mc.txt.text = i+1;

     mc.x = (mc.width + space) * col;

     mc.y = (mc.height + space) * row;

     addChild(mc);

          if ((mc.txt.text == rowCount/rowCount)||(mc.txt.text == colCount)||(mc.txt.text == tileCount-colCount+1)||(mc.txt.text == tileCount)){

               mc.gotoAndStop("corner");

          }else if ((mc.txt.text < colCount) && (mc.txt.text > 1)){

               mc.gotoAndStop("topEdge");

          }else if ((mc.txt.text < tileCount) && (mc.txt.text > tileCount-colCount+1)){

               mc.gotoAndStop("bottomEdge");

          }

}