I am one of the pioneers that came before.
A rare breed a old bold diver. There was nothing beyond basic when I started and all the advanced type diving you learned by doing, if you had the testes. I wasn't about to spend my time and money after 10 years of diving to take a AOW class. I just kept diving until 1992 when various things prevented me from continuing until this year. My only regret is that I didn't log many of those dives and the log I had I can't find. I'll probably take some kind of AOW/Nitrox training so I can travel and dive. These days it seems that's the only way one can do it. Thanks for your concern but it's not necessary I do just fine for a old man.