How unlikely is it for a experienced hair transplant surgeon to extract (FUT) hair from a non-safe donor area?

Hello Doctors, Just wondering from personal experiences having performed thousands of transplant procedures how likely it is for an experienced Surgeon from a good clinic to extract hair from a non -safe donor area , Particularly when the head is completely shaved Prior to making incisions? Id imagine it would be vey unlikely , how do you all clearly differentiate between the " invisible line" of safe and non safe? my 1st transplant hairs were healthier looking 2 years than now