Do the certifying agencies recognize each other's courses? I'm SDI certified, one of my neighbors is neighbor is SSI and another is PADI. My dad is NAUI. We are all interested in Nitrox certification. Do all 4 of us have to do it with our own agency? If so, that seems a bit goofy. For example, if I took the Nitrox with SSI, PADI or NAUI, could I sent that documentation to SDI (along with the $15) and get my C-card updated with SDI?