This is the second instance in a couple of weeks of someone expecting to get into a partner lounge without even a BP. This doesn't fall within the rules, and why do people expect them to be bent so much? This is honestly the OP's fault (or his TA's, more accurately) for booking him on a routing that carried this inherent problem. You were on two separate PNRs and weren't UA's problem until you were checked in, according to their hours of operation at SIN. I'm sorry but I think that you are asking for way too much here.