I was turned away from the KE lounge in MNL when arriving on a CO Micronesia flight. I didn't fight it too hard, as my wife didin't really want to deal. And the "most" caveat lets them do whatever they want.

I had similar experiences as a *G (also supposed to have access to all partner lounges) on our recent NZ trip, particularly in SYD where both the NZ and SQ agents said "you know that the UA lounge is downstairs, right?" After explaining that I did know that and that I also knew their facilities were better I was granted admission. FWIW, the NZ lounge is actually better in SYD but not the SQ.