And, based on experience, so do I! But Tango's entire development has been based on that informality. Whoever thinks they have enough knowledge can teach, or in many cases other people, potential students, cajole someone into teaching or coaching them. Of course ad hoc teaching/learning is inefficient. Human evolution and development was/is very inefficient, that's life. Talking about efficiency starts alarming thoughts of bureaucracy and autocracy. I think not! Tango was evolved informally over many years and its worldwide spread is causing another evolution, part good and part not so good. But thankfully Tango is alive and not pickled into books of steps and tiers of diplomas.