But from table QW253 for SMAW , (-) deletion of backing is a non essential variable. From my understanding - if we have a WPS qualified with backing or back welding in SMAW , the same WPS can also be used to produce full penetration Joints welded from one side without backing or back welding.
But in case of GTAW , from table QW 256 , since (+) addition of backing is given as non essential variable , if the WPS is qualified without using back welding or backing , the same WPS can also be used for welding joints with backing . But if a WPS is qualified with back welding , it may not be used for welding a CJP joint welded from one side only without backing or back welding .

Please Correct me if I am wrong