They have an internally published policy of not permitting *G to access their SFO lounge except on international itineraries. (And I've read reports of similar policy being applied at other outstations as well, but can't remember the specific details.) That is directly contrary to *A rules. They will also arbitrarily deny access at various lounges to *A or business class pax who are not flying SQ. For example, TG J pax have reported denial at SIN SKL.