My top band will be able to play grade 2 because we regularly play grade 3-4, but this is not common around the state. Our non-varsity bands are going to start like beginner classes. They will struggle to even play grade 1 well. Not so easy to generalize your scenario, though I agree there are pieces on each list that may well qualify on an easier list. I would hate to judge a contest where every band played Abracadabra and Colliding Visions!
I would be in favor of going one grade easier for each piece. But I would add that bands who are required to play two grade 1 pieces should be required to play one grade 1 and two "director's choice" selections. And write a level zero sightreading piece.
My two cents. Good luck everybody!