There are three files for each texture. The diffuse, normal, and RAH. I assume they are roughness, specular, and something else compacted into a single Targa.
Best guess… Roughness Alpha and Height?
Probably A = Ambient Occlusion
Roughness, AO, Height, Normal and Diffuse/Albedo == 99% since most things are either 1=metallic or 0=not (no point adding a map for rocks you dont need i.e. Metallic)
Cheers