On my return flight from Taipei to Shanghai booked with Delta points on China Southern, I was charged for excess luggage fee ($80 USD) by the China Airline agents. I at that time was Skyteam elite member and was told the fee still applies. I was never charged for excess luggage when I checked-in in Shanghai airport.
A side story, about a month ago, I was travelling on Air China from Taipei to Shanghai again, I was checked-in by China Airline agent. They were so cheerful when they noticed my luggage was overweight, all of a sudden, she commented that because I was *A Gold, I am entitled to extra 20K.
So better watch out next time you are checked-in by China Airline agents.