Regardless of how it is stated on the bill, I would view the sum total of both add-ons as their service charge and be done with it unless one wanted to leave something extra for the server.

Some places on the island have been known to show the TOT (turnover tax of 5%) on the bill or verbally state it is part of the service charge, which is supposedly not how it is to be done. When they do this I factor it in as part of the total service charge. Once anything resembling 15% is added to the bill on Dutch SXM, it IS a service charge.