The Comorbidities Elixhauser profile is modeling the components of the index.  Inclusion of the index is supported, but not required. We will modify the document that the index value SHOULD be present, and explain the circumstances where the index value could be missing. Two situations where the index value might be missing are (1) when the standardized comorbidity components are themselves of interest and the index is not, and (2) If the components have been collected, but the index has not yet be calculated. In the second cases, the observation might be sent across the wire to a server that fills in the index value, so in the interim before that, the value is missing.