Are you sure about UPS21...because for one it shows the departure date as tomorrow and while I know it is tomorrow in China, the scheduled departure time was 1 hour ago and it hasn't left...I use flight aware and if it were delayed it would have said so
The problem is, FlightAware ONLY updates flights that are located within certain boundaries in the ATC reporting system in the US.
It will say on that page in red "At least part of this flight occurs outside of FlightAware's service area. Information on this page may be unreliable."
This means that (like I said) until about 3-4 hours out from Alaska, NOTHING will update on that page. After that time, it will update. Trust me it left bud, don't worry I have watched international flights before and I have watched about 10 of these flights in the past few days