In material database editor of CII, Yield stress values are filled with different values corresponding to the reference temperature
ASTM or ASME Code just indicates a single yield stress value for each material.
I`m wondering which code, database or calculations are used in CAESAR II database.

Broken,
I didn't look up all the codes, but I think you can find the table of yield stress(also strength) at temperature in ASME BPVC Sec.II