Sandia PV array performance model - correct equation

Hi, I am trying to build Sandia PV array performance model in Excel. I have a question regarding the temperature coefficient of short-circuit current (Isc).

The model (in the SAM PV Model Technical Reference) uses Alphasc,ref i.e. temp coeff of Isc at reference conditions (usually STC). Whereas, the model in the paper by King, and on the pvpmc.sandia.gov, uses the normalized temperature coefficient for Isc i.e. alphasc,ref divided by Isc0. Would anyone know what is the correct value/equation to use?

Thanks so much!

Regards,
Ankur