If IDists can discern design from nature in DNA, we can certainly discern typos. Or to put it another way, if we cannot, because of our human limited understanding, discern typos in DNA, what chance does ID have of discerning design from nature, especially since a designer could make design appear to be nature, and nature could very easily appear like design?
Hmmm... déjà vu:
If a living system looks well designed, it's evidence for ID. If it looks poorly designed, that's just because we have no way of knowing what constitutes good and bad design. (from The Quixotic Message)