It appears from the spec we are not missing anything. The obvious way to encode a format component count is in the dword which specifies the type of each component. Those beyond the last component could be D3D11_SB_RETURN_TYPE_UNUSED, but instead they all have the same type. There's no other place to store it. The output from /dumpbin has four components for the declaration too, and the load instruction specifies a vec4 load. Looks like the actual format component count is left out.