Goal.AchievementStatus cardinality is 1..1 (Required element) should be relaxed to 0..1 to accommodate situations where a goal is documented but the process to achieve the goal has not been initiated. Also, making the element required does not align with the Goal.LifecycleStatuses - proposed or planned. 

A 'planned" or "proposed" goal will not have an achievement status yet. Keeping the cardinality as 1..1 will force the sending system to add a null flavor based on the MustSupport and Missing Data guidance. Use of null flavor in this situation is not necessary because the data is not missing. In this situation, the data is not needed.