Actually the number of bags and total weight don't matter in current policy at most airlines. A single bag overweight will attract a charge even if the total is below the maximum! Up to the pax to redistribute weight between bags or purchase a new one. Most of the Oneworld airlines have an informal policy of extra allowance of some sort for OW status; as mentioned on AA it is to waive the per-bag fee for up to 2 bags (worth USD 50 per sector). So on AA you can take 46kg for free (but max of 23kg per bag); single bag of 24kg will cause a charge (about USD 50) and it is to the ounce.