Thanks again for reply! In answer to your questions
1) Absolutely no significant trauma to the shoulder that I can remember. I am/have been an extremely active person from young age. Swimmer, competitive skier, fire fighter, competitive mountain biker, weight training (nothing too outrageous - just for sports fitness), Lots of sets of pull ups, river guiding...just a full active sports life. Doc said that even with that much activity my shoulder situation is odd (don't like to see that quizzical expression on your doc's face...) Many people live full lives working in hard physical jobs, weight lifters etc and they may get soft tissue injury but usually not shoulder cartilage stuff unless there has been trauma or systemic illness.
2) Plural "doctors" because, yes I did have my surgery at Stanford - so teaching hospital. There was the "fellow" and the main doctor who is a well respected sports orthopedist who did his own training with Steadman in Colorado.
3) At this point even the doctors cannot explain why this happened...sometimes even the experts don't know unfortunately. I have asked several times and they really, honestly are not sure (frustrating). These are excellent doctors I have also, if anyone should know, they should. I have access to many pub med journals because I am getting a masters degree currently. I have tried to look for the various reasons that random cartilage defects occur in an otherwise healthy person with no significant trauma. This is also my non dominant arm which is good but odd also. I have had other sort of mildly odd cartilage stuff in last few years, so one doc thinks that maybe my cartilage genetics are not the greatest (not the worst) but enough so that my very active life is causing wear and tear that is not normal. Sometimes it is very hard to accept that there really is not a clear answer because so often there is.