All the base metals listed in D1.1 are carbon or high strength low alloy steels. From the welder's standpoint, one welds much like another.
D1.1 does not consider the base metal, provided it is a listed material in table 3.1, to be an essential variable for the purpose of welder performance qualification.
Using AWS D1.1-2008 as an example, Table 4.12 lists all the essential variables that pertain to welder performance qualification. Note that base metal isn't an essential variable listed. Once the welder is qualified for any listed base metal, he is qualified to weld any base metal listed in D1.1.
Earlier editions of D1.1 are clear on the subject. As an example, D1.1-94 opened clause 5.16.1 with, "Qualification established with any one of the steels permitted by this Code shall be considered as qualification to weld or tack weld any of the other steels."
Change isn't always for the better or necessarily an improvement.
Best regards - Al