The difference between an SA versus A designation has to do with ASME Boiler and Pressure Vessel code endorsement of material. If a material is supplied to an SA material specification, this material meets the requirements of ASME Boiler and Pressure Vessel Code, Section II, and can be used in code-fabricated items. If a material is supplied with an A designation, it meets the requirements of ASTM.
In some cases A and SA material designations can be equivalent, in other cases they may not be equivalent with material that is an A designation not even permitted for use in code fabrication. So, review ASME Section II, Part A Acceptable ASTM Editions.