Rick,
You will notice that in table 4.1, that the base metal essential variable says that for unlisted material, a change in "base metal type" requries requalification. So the question is, what is the definition of type? I get that from paragraph 1.2. It lists 6 "types" of stainless steel base metal. 1. Austenitic, 2. Ferritic, 3. Martensitic, 4. Precipitation hardening, 5. Duplex, and 6. Dissimilar. Under dissimilar, it says "any combinations of the types above or with weldable carbon steels or low alloy steels."
So when I qualify a procedure using for instance, austenitic stainless steel to weldable carbon steel, it seems to me that it is ok to use it to weld to any other weldable carbon steel since that is listed as a "type" in paragraph 1.2. Similarly, since none of the precipitation hardening (PH) stainless steels are listed, a procedure welding carbon steel to PH sst to carbon steel is good for any weldable carbon steel to other PH stainless steels. It does obviously require use of engineering judgement to make sure you don't use procedures where they are not adequate even if they are qualified.