Originally Posted by MSPeconomist

Your guest need not be on the same PNR as you, but the GM+ on international itinerary would seem not to apply if you have two itineraries on the same day and are trying to access the lounge around segments on the domestic ticket/itinerary rather than with flights on the international itinerary. For example, suppose I fly EZE-ATL, arriving about 6am on one ticket. I spend the day in Atlanta and in the evening fly ATL-DTW-MSP on a different PNR/ticket that has no international segments. Without a SC membership, Reserve card, or AmEx Plat/Centurion card, I would not expect free lounge access in DTW.