Should they be tagged with both c++ and the derived language? Or should they be tagged only with the derived language?
If there is syntax or entities in the question not present in plain ol' C++, then the question should not be tagged c++.
If there are no such entities then it is probably a completely general question and likely should not be tagged with the variant. Exception: if it is possible that the answers will require non-standard tools. In which case the tagging should be revised.