The ait-1 invariant requires that the clinicalStatus element must be populated if verificationStatus is not 'entered-in-error'.  But populating clinicalStatus is not appropriate when representing cases of "no known" allergy, as something that is "not known" can neither be clinically "active" or "inactive".  If a "record status" element (e.g. AllergyIntolerance.status) element was available it could be populated in these cases, but currently that does not exist in the resource.