Originally Posted by MSPeconomist

You're right. I also swiped my way into CO lounges at times, although this could be problematic when CO and NW (or DL) were close partners in that the dragons tended to enforce the technical rules so that there were lots of surprise denials. For instance, if one takes a RT between MSP and IAH, MSP had only PMNW lounges while IAH only had PMCO lounges. If you wanted to purchase a RT ticket to save money, it wasn't possible to get MSP-IAH on PMNW and IAH-MSP on PMCO so as to have lounge access at both ends before your flight. It could be very frustrating, although IIRC there were periods when PP might have solved the problem in one direction.