Dual certification of certain, overlapping material grades is permitted by ASTM. Check the chemistry and mechanicals on the test reports to ensure correctness for dual certification.
The dual grade material is the material has the mechanical and chemical properties meet the requirements of two types of steel. Both grades will be stamped on the material.
The standard A860 is more strict in both chemical and mechanical requirements, you can use WPHY 42, 46 and maybe WPHY 52 as WPL6 , when the tensile strength is not over 95 ksi, the yield strength,elongation and charpy values are lower for WPL6 with not maximum values. The WPL3, WPL8 and WPL9 are different material, the chemical requirements are different. About the marking all depends in the supplier and customer agreement