All though I hold welders in high regard, the decision to meet Class A, B, or C in the case of D17.1 or the requirements for static nontubular or cyclic nontubular/tubular for D1.1 is not the welder's to make. The welder has no idea of what loading conditions have to be met.
If there is any question, the customer (or design authority) should be consulted. If no response is forthcoming, bid the job to the most critical requirements and meet those more stringent requirements to be safe. The acceptance criteria is different for the different weld classes and the NDT may be different as well. Better to be prepared than to get caught with your pants down.
Best regards - Al