It's a bit confusing to me, but as near as I can tell (and someone please correct me if I'm wrong):
- The UA website seems sometimes to omit award availability on flights that Air Canada (AC) or All Nippon Airways (NH) website(s) show as available.
- The AC website seems sometimes to omit *A award availability if AC flights are available to fit the search criteria.
- The NH website doesn't seem to show Swiss (LX) availability (When did LX join *A? - perhaps not loaded yet?)
So you probably want to check each.
As for Expertflyer, IMHO: among *A carriers, only AC's award code(s) are shown.