As noted above Variables differentiate between Substantive and Sentinel representations at the point of reference hasSubstantive..., has Sentinel..., Capture simply has "hasResponseDomain" (0..n). If there is a need to differentiate between these two types and it is not done at the point of reference (relationship) does it then need to be on the Response Domain? If so, is it something simple like a flag "isSentinel" xs:boolean?

Note that this relates to DCAT-13 which you closed by removing the Sentinel and Substantive Value Domains. It seems you need them, maybe just not where they were provided.

This should mirror Variables in terms of using Substantive and Sentinel response domains