As with anything, ZED tickets are only as good as the knowledge of the check-in agent. I am customer service with BA in EWR and tried using a ZED ticket with AA in SFO. Ticket was issued SFO/MIA valid ZED/AA. Wanted to go SFO/JFK to connex with a flight to EZE. SFO to MIA or JFK is in the same fare band. AA said I needed to reissue tkt to say SFO/JFK. Even the supervisors had no knowledge of the ZED program. By the time the BA tkt counter opened, we missed the flight and opted to fly BA from SFO/LHR/EZE. Only lost one day of vacation, but had a wonderful time!