Question: Am I missing something? I do not enjoy holding up production by rejecting procedures that have been in use for years but how can you list backing material as weld metal and have the only process listed as SAW with a root spacing of up to 1/4" on single Vee groove welds? The weld metal you mentioned could be a “backing weld” which is backing in the form of a weld, the purpose is similar to baking bar or back gouging.
Your main interest is to determine the weld thickness made of SAW minus the backing weld thickness. A WPS qualified using a test coupon with backing in the form of weld is also qualified to weld with backing bar or back gouging.
If your weld production requires one side welding without backing, then you will need to know the applicable WPS for the root pass which is appropriate for the 6mm root gap (1/4”). This WPS is not necessarily to have a combination of two welding processes.
Be careful with the reputable companies, they are not s****d. When the project is delayed, they will use your bad call as scapegoat. When there is an independent expediter, it might be reported that the delay was due to incompetency of the client inspector or 3rd party. This will lead to termination /or replacement
~Joey~