Originally Posted by
Microwave
oneworld rules would not permit lounge access for someone flying on a solely North American itinerary, such as JFK-YVR, BOS-JFK-YVR or the like. It's very possible that the people staffing the lounges at T7 are unaware of these restrictions, or are intentionally disregarding them, but the alliance's lounge access rules carve out a specific exception for such flights, and any exceptions should be considered gravy.
Or CX has made arrangements for all premium elite pax to use the BA lounges at T7. Cx is othe mindset that they need to offer lounge access to premium and elite pax wherever possible, regardless of ow's AA-inspired rules. While what you state are indeed the OW rules, OW carriers beyond AA don't make a distinction for domestic or international flights for lounge access.
Another example is the qf108, JFK-lax. While you need to be on an international itinerary to fly this flight, those international segments could be months apart from your domestic journey. If you're in j, or have an emerald or sapphire card, you'll get lounge access on both sides of your purely domestic flight.