OK folks, let me try to explain(though Radar is right).
The BOW's draw length is the distance between the grip (or the "plunger button hole" if you prefer) and the string when the bow is at full draw. Adding a string loop doesn't change the distance between the grip and the string, so it doesn't change the draw length of your BOW.
Your "Correct Draw length" is the draw lenght of bow YOU need so that the string comes to a consistant and comfortable anchor point when YOU draw it. If your anchor point isn't comfortable, then you need to either change the draw length of your bow, get a different bow, or change your anchor point.
So if you add a string loop to your bow, and you want to keep the same anchor point, you need to adjust your bow to a shorter draw length, so that the string stops a little bit short to make up for the distance between your release on the loop and the actual string.
When you add a string loop to a bow, the bow's draw length doesn't change, but your correct draw length for a bow with a string loop is slightly shorter than your correct draw length for a bow without a string loop.
When I went from finger shooting to a release I shortened my draw length by 1.5 inches (new bow), and when I went to a string loop I shortened it another half inch (cam module adjustment).