To provide the user with the date when an item was published, and for administrators to determine the age of the resource
A single year is the preferred format. For more precise dates, use the ISO format without the time value: YYYY-MM-DD or YYYY-MM.
Although the field is optional, it is often useful when a clear Temporal Coverage value is not present. For example, one may want to preserve a dataset with an uncertain lineage, but there is an indicator on a data portal on the date of last update. In most cases, the 4-digit year is sufficient.