A birth record tells you when a branch began. An exposure log tells you what kind of world it has survived. For the Children of Luna, the second is often the more meaningful civil document.
Exposure history records the stresses that shape judgment, wear, caution, and adaptation. It is often a better guide to maturity than simple chronology, especially in colonies where one year can contain far more strain than another.
This is why some branches treat exposure logs almost as public character records. They explain what duration by itself cannot.