don't allow them to retain and share outcome data for off label use of medicine so that their decisions can be evaluated collectively

By whom? Who checks the data, who ensures there are no confounds, who evaluates and who concludes? Doctors already report unusual problems with medications, which is how we discover the drawbacks of drugs that somehow made it through the incredibly stringent gauntlet of drugmaker testing. *cough*

I think you're also grossly overestimating the concern doctors have for ensuring their patients are getting proper treatment. It seems to me that most doctors, like most patients, want to believe that what they're doing is effective, and don't want to doubt. So they don't, and take the choices they make for granted.