Originally Posted by
RedChili
To me, this does not make sense at all. Several airlines have different lounges for C-class and *G, such as SK, LX and SQ. According to this theory, when a C-class passenger with *G is flying SK, LX or SQ, it's the choice of the lounge made by the passenger which determines who will pay the bill. SQ actually has better lounges for C-class than *G. So, if a SK*G flying SQ C-class decides to use the C lounge in SIN, then SQ pays, but if he decides to use the *G lounge, then SK has to pay SQ?
Actually, if you go to the Krisflyer Gold lounge with an SQ J ticket, expect a certain level of resistance, and encouragement to go to the Silverkris Lounge instead. Same for coming with another *A carrier J ticket.
I did not say it made sense. Nor that I have every part of the picture, as that is generally not public information. So take it as guiding principles, but the intricate details of very specific cases as you list above, there is no knowing.