DV accepts any format (dd-mm-yyyy, yyyy-mm-dd, mm/dd/yyyy, UNIX timestamps, etc.) as long as it is clearly documented and consistent.
It is better to be as specific as possible. So, if available, use full dates (day, month and year) instead of only the year (or year and month).
In some regions, the term "build year" is used when referring to the year a vehicle was first registered, instead of the year when the vehicle was constructed. To avoid confusion, it is preferable to use the terms "construction date" and "first registration date" instead.