The C-CDA R2.1 schematron and Companion Guide schematron both prohibit a Medication Activity's substanceAdministration/effectiveTime from having a nullFlavor, which seems incorrect; for instance, you might want to send one of these in the empty substanceAdministration for the case where the patient has no known meds.

Maybe this is kind of moot with the impending move to 3.0 but I figured it was at least worth discussing.