Clause 7.6 describes the elements of the specified substance stratum, PhPID_SpSUB_Lx. The public contents name the same five subclauses as the substance stratum: the construct, the specified substance set, the administrable dose form, the unit of presentation and the medical device. The parallel structure is the point. The stratum is not a different identifier scheme; it is the same assembly rule applied to a different starting element. That means an implementer who can build the substance stratum already has most of the machinery, and a data model that can hold one can usually hold the other. The element definitions and the construct rules are not in the public preview and are not stated in the text we hold. The public FDA material describes the specified substance stratum as one of the two strata used for the identifier and confirms the parallel four-level construction.
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.