The "stiff side" he is likely refering to is perhaps where a layer stops/starts (?). I've also read where some people plug the ends and float them, supposedly any heavy sides will end up down, I don't know much about that. I bare shaft all mine first. If you have most of them going to the same spot and a few that won't, take those few, and try rotating the nock a 1/4 turn and retry. Keep going 1/4 turns and see if it will come into the rest of the group. Once they're all going in the same place, then fletch them.
If they're already fletched, and the arrow won't play nice with the others, rotate the nock to a "new" odd feather and re-try. If it just won't group, change out the nock and see if it mkes a difference.