When I did my OWC dives, my partner was a NAUI transfer guy from the local college. He had done his pool and classes through NAUI at the college but was being certified by my instructor who was SSI (not sure on all the details). Anyways, this guy was the absolute worst diver I’ve ever seen. During OWC he failed to turn on his tank before a giant stride into the water, he flailed like a fish when mask clearing, he could control buoyancy and was constantly silting it up. I tell you this because I also have friends who are NAUI and are some of the best divers around. Moral of the story, Certifying agency doesn’t matter, what matters is the instructor and unless you can’t figure out the difference in your first and second stage. Theres no reason to recertify.