Targeting movieclip dragged on stage

1

First let me say I’m relatively new to AS 3 and I’ve scoured the Internet looking for a simple solution to no avail.

Here’s my general situation:

  1. I have dragged a movieclip with an instance name of a_mc onto the stage.
  2. On the first frame of the timeline I am importing a class file and calling its constructor:
import cardmaker.*;
var coverMaker:CoverMaker = new CoverMaker();

I was under the impression that since the movieclip (a_mc) is already on the stage that I could target it from within the constructor function just by name, however, I always get a “1120: Access of undefined property a_mc”

Simplified Class:

package cardmaker {
    import flash.display.*;

    public class CoverMaker extends MovieClip {

        public function CoverMaker():void {
        
            a_mc.gotoAndStop('on');
       }
    }
}

With this problem in mind, is it “better” to just dynamically position every Library object on the stage instead of dragging them manually? If so, what is the benefit?

Thanks!