Thank you so much for your help!
So for example if say hypothetical flight 1850 was able to be booked for pax on us airways, if an employee wanted to non-rev on that exact same flight, it would be zed fare since even though it's booked (by pax) on US it's operated by BA?
So if it's a codeshare operated by lets say BA it's zed fare, but if it's a flight actually flown on US or AA metal, it's regular standby right? I think I understand it now. So if I want to go to say Europe w/o Zed, i'd have to get a flight operated on US or AA metal and not a codeshare.