"My" circumstances were that my wife (gold) was seeing off her sister at DXB and tried to use miles to upgrade her from a saver Y fare at check in desk and was denied as she was not on the same flight. As stated earlier if upgrade inventory is available when the 24 hour OLCI window has opened then you can do it through Manage My Booking by having the member log in and access the booking for relative/friend before OLCI is performed and it works fine. That is what we did next time round.