AMS Turnaround on SQ
I had a uneventful SIN-AMS-SIN turnaround last year. There's plenty of time before the turnaround so I exited immigration had a look around the airport before the SQ checkin counters opened. Was first in line to get my AMS-SIN boarding pass. I had a *A gold card, but used a non gold *A card to put my miles on for which I was in the process of getting gold status for. I mentioned to the check-in agent I had a *G card, so where could I find the SQ lounge? Strangely he wanted my *G card to input the number. I was afraid he would change my miles to this card, but he assured me he was not.
With my boarding pass in hand, I proceeded to the SQ lounge, though it still wasn't opened, so tried out the Priority Pass lounge next to it, which was quite horrible. After a bit of time, the SQ lounge was opened, so I went in there. A small cozy lounge but nicely done and I had no problems passing the time there eating breakfast and using the internet.
At the gate I found the reason why the check-in agent was so keen on getting my *G card number. I was upgraded from Y to C based on my *G status. So a very pleasant surprise.
Given the long turnaround time, I don't think anyone will have any problems doing a AMS turnaround on SQ.