There is another Forum type website that has a lot of good information and is called Eng-Tips Forum. The link is
http://www.eng-tips.com/viewthread.cfm?qid=130771&page=8The following is about the best explanation I have seen on the A versus SA or SFA, between ASTM, AWS and ASME. The post is attributed to a guy with metengr (Materials) as his identity.
"To add to the above, when the ASME Boiler and Pressure Vessel Code was formed, a materials subcommittee was established to review other materials standards/specifications like ASTM and either adopt them in whole or in part, with exceptions or editorial revisions.
To assure identity, the ASME Code committee elected to use a prefix S to denote that the material specification was reviewed and approved for ASME Boiler and Pressure Vessel use. In some cases, material can meet both ASTM and ASME specifications. In other cases, ASTM materials are not acceptable for use in boiler or pressure vessel applications."
For welding fillers, ASME took the AX.XX from AWS and added SF to the front, making it SFAX.XX.
Hope this helps.