Originally Posted by LyingFlat

From my understanding, *A rules allow individual carriers to implement their own policies when it comes to *G benefits on itineraries that are solely their own metal. This is the case with various "Light" fares (no baggage) offered by the LH Group, UA domestic having no lounge access for it's own UA*G members, and NZ's Seat Only fares no giving an extra piece of luggage for *G. However, where an itinerary has 2+ *A carriers, the rules generally require airlines to accept an additional piece of check-in luggage (an exception may apply to LH/LX/OS/SN Light fares as they are part of the same group).

I remember many years ago a ticketing error permitted an end-on-end combination between an LH Light fare (no baggage) and an NZ Business fare (3 pieces). The passenger was NZ Elite and his itinerary was AKL-LHR in BP on NZ2 with a few days in London. Then LHR-FRA on an LH Light fare. He had 4x checked bags - 3x as Business + 1x extra as NZ*G. No issues with a 4th bag at AKL due to 2+ *A carriers, but a big fight with LH at check-in in LHR. LH ultimately had to accept all 4 bags as both they and NZ were on the same ticket - plus, USDOT and MSC rules also applied. If he wasn't *G, then they would've only had to accept 3 bags.