I haven't read all 80+ posts, but I am bored today and find the question interesting. It seems to me that regardless of whether some agencies issue Solo Diver certifications under their "recreational" rather than "technical" umbrella, a more useful dividing line is whether most dive operators consider a Solo card to be a threshold requirement--that is, a ticket--for divers to dive solo with them. The OW card is clearly a threshold or ticket cert. In contrast, AOW, Rescue, even DM usually are not required by dive ops before they will let you do a dive. I know there are exceptions, but in many places in the world, a diver presenting an OW card will be allowed to do the same dives as a diver presenting a Rescue or DM card. Likewise, most specialty certs are not what I would consider a threshold or ticket cert. Recreational Nitrox is one, but I think Nitrox is an exception--it really should just be part of the OW course. Really, with few exceptions, the only training that dive ops consistently require for them to allow a diver to do just about any OW dive with them is the training represented by the basic OW card. Beyond that line, I believe it is reasonable to consider every threshold or ticket cert to be "technical." Cave and other technical certs clearly fit this description. So, presuming that a Solo cert is something that most dive ops require before they will let one dive without a buddy, then it seems reasonable to me that a Solo cert should be grouped under the "technical" umbrella. Now, I have no idea whether that presumption is true or not. If it's not, then it seems reasonable to me to group Solo under Recreational. Just my take on it.