Bosley did not provide you with a written guarantee. One of their doctors verbally said they "will stand by you" which means nothing in a court of law and means nothing outside either.
Phil,
Not sure if its legal binding but they did give me a written guarantee which states: "THE BOSLEY GUARANTEE-For all hair transplantation procedures performed at Bosley, we guarantee to replace any non-growing hair transplant graph free-of-charge, providing only that the patient has adequate donor hair. In our experience, such replacement has seldom been necessary."