I found out the hard way that there is one big difference between *A and OW on excess baggage rules when flying on a partner airline:
On *A, if travelling on a partner airline (e.g. I (NH*G) travelling on SQ) my excess baggage privelege as NH*G will be accepted at other *A airlines.
On OW, it is different. I flew on CX as a JL (One World Sapphire at the time). I had 28kgs, and the friendly but strict checkin agent at CX insisted I pay 3 kgs excess charge.
She said that on OW, the ONLY 2 things recognized for a OW Sapphire on another airline are lounge priveleges and mileage accrual. She specifically said that the excess baggage rules are different between *A and OW.

Is this correct, or was CX wrong?