Most of the Observation based profiles don't explicitly call out the .dataAbsentReason element but the Body Mass profile includes this element with a cardinality of 1..1. Why is this profile different? Is the Body Mass profile required in some of the program specific bundles? Also, given that it's cardinality is 1..1, does that mean it needs to be in every resource and if so, does that make sense? Or is this a "Must Support" type of element rather than always required? Please clarify the importance of including this element.