We didn't really have a 2nd or 3rd NT in 2003. We had Ted Washington, and then I guess Seymour could have played it (but it wouldn't have been the best use of him IMO). No one else on defense was bigger than Cowart, Guy, Parry, etc. Now, Shelton is NOT Washington, but for depth purposes, we're in a similar boat. And that team was 4th in rush defense (6th in YPC against). Other than 2004 when we had Traylor and a rooki Vince, I'm not sure we've routinely had two great NT on this defense in a long while.
If I'm missing a duo, let me know. This is more an exercise in my own memory than an attempt to prove anyone's opinion right/wrong.