I don't know if I am doing something wrong but this neat trick seems to be working for me only on the international flights or maybe on CO operated flights only. I happen to have the same CO51 flight coming up in Feb and I can clearly see myself on the confirmed UG list. However, I can't see this info for any of my domestic flights (which all happen to be on UA) other than for the flights within 24h of departure. Therefore I am thinking that it works either only for CO flights or only for international flights (or some combination - don't have time to investigate)