The protective clothing works against both mustard gas and sarin. However there is the argument that sarin enters mainly through the lungs but is not that effective against skin. A combination of sarin and mustard gas would force a soldier to completely suit up rather than only wear a gas mask to protect against sarin.

I just checked a website on chemical weapons and found that mixing sarin and mustard gas was in fact standard Iraqi operating procedure. My original suppossition that sarin and mustard gas mixed indicated discarded chemical weapons was not correct.
Gary