The corresponding function for the saturated liquid entropy without using the Limit function seems to work fine.

sSatLiquid[t_] := Module[{psat},
  psat = ThermodynamicData["CarbonDioxide", 
    "LiquidVaporPhaseBoundary", {"Temperature" -> 
      Quantity[t, "DegreesCelsius"]}]; 
  ThermodynamicData["CarbonDioxide", 
   "Entropy", {"Temperature" -> Quantity[t, "DegreesCelsius"], 
    "Pressure" -> 1.0001 psat}]]

Thanks! NLimit is the answer. (Heel of palm to forehead)

I believe m=1 would work for saturated vapor, but what about saturated liquid?

Thanks again.