In my understanding the "Not interpreted" case would be just a text string "DateTimeSourceText", repeating whatever is written in the label about the dates and times. This can be useful if questions arise of the interpretation. Btw., isn't he name of the element "EarliestDateCollected" in Darwin Core v.1.4 proposal a bit misleading as it really is "EarliestDateTimeCollected"? Hannu Richard Pyle wrote:

RE: CollectingDatesInterpreted When would this field *not* be set to true?