Allow looser rules for dates
Approximate Start Date
Values may be just a year (e.g. 2026) or a year and a month (e.g. (2026-05). If the full date, i.e. year, month and day, are known use ceterms:startDate.
The value should be in ISO 8601 date format; specifically YYYY or YYY-MM.
Approximate date the validity or usefulness of the information in this resource begins.