In 2003 the material information shifted between A 108 and A 29. A 108-99 has those GXXXX designations. In A 108-03 all those are gone. Maybe ASTM decided having the grade designations in both standards was redundant.
Actually, the way the example ordering information reads in A 108, they encourage you to use SAE numbers rather than grades of A 29 (even those are SAE numbers), but yet the text of A 108 says you want to refer back to A 29 for your composition. But I digress.
Hg