I thought the same. I have done stuff that would be considered advanced tech diving in recreational circles, but because I didn't take a NAUI/PADI approved course "you're technically not allowed to do those things." That is what the local dive shop instructor tells me. They are too concerned with lawsuits and safety I guess. If you ever had the certs from NAUI/PADI, then you can do anything no questions it seems. If they came from the military or commercial sectors, then you'll have to find out about some kinda crossover, but I didn't have any luck converting my experience into automatic NAUI ratings. So if I want the offical NAUI Nitrox, my previous experience won't grant me the rating, but after I have the rating the experience is all valid. You will have to check with the instructors at your dive shop. Some of them are cool, some are uptight and by the rules. Refresher courses aren't even offical courses. You can do your own basic refresher. All they do is review skills and dive tables. You're paying for the instructor's time to answer questions more or less. Explain to the instructor that you had the training in the military, and want some refreshing in new technique and review the text. I don't see a problem, but you never know. Every instructor is different. A c-card and ratings don't expire, and don't have to be renewed. If you are going with guys that already have a mixed gas or tech cert, then have them get your tanks filled, help with dive planning, etc. Really, what law will you be breaking if you go deep diving and don't have that rating? It's about experience. That's how I view it. You should be fine. I wouldn't worry about anything. For me, I just want to be an everyday single tank diver again. I want clear, warm water with viz. Hobbies don't make for good careers as I found out. You sound like you're in the same boat I am. Being a regular old scuba diver, but maybe add a little spice with a wreck dive in deeper water or something like that. I got burned out on blackwater, long bottom times, and three hours sitting in a chamber.