One thing everyone needs to remember here is that in some cases, longer questionnaires rather than classic scores like GCS or ABCD etc, can be in a state of partial completion over some time period. Therefore, marking unanswered questions with null flavours probably should only be done at a final completion step. openEHR already has a lifecycle that allows partially completed content to exist and to be committed to the versioning system, i.e. there is no problem committing a half-done questionnaire so that it is visible to carers; it can be marked incomplete.