Set ticks to GUID. Could use it to store date dimension in GUID, or add another dimension: date -> period -> createdAt: e.g. today at 3PM (creation date) we learn that yesterday (date) fact A for period P was at X1, but at 5PM (createdAt) data source says that there was an error and the value is X2. Never overwrite any data point, everything persistent should be append only.