Status quo:

Upon connection establishment, a Client passes InputVariables or InputGroups and / or OutputVariables or OutputGroups to EstablishConnections, that will be referenced by the created ConnectionEndpoint.
It also passes PubSub configuration (and in the future C/S configuration) that maps these variables on the communication layer.

Problem 1) A Client may pass variables to be referenced that are not contained in the *DataSet it passes (or references if preconfigured).

Proposal: EstablishConnections shall issue an appropriate StatusCode, if this condition applies. According to current specification content, this would be a Bad_NoMatch in the CommunicationLinksResults.
Further action on this can only be taken after 0007720 is clarified.

Problem 2) A Client may pass variables to be referenced, but the passed or referenced *DataSet contains additional variables.

While this is not a use-case that was discussed, it also does not constitute an error per se. From an FX point of view, the publication or subscription of certain variables in the FX model have been requested, and these are mapped on the communication layer.
Whether additional variables have been added to the DataSet (which may be consumed by non-FX devices or applications), does not constitute an error.

Proposal: no action required.