GlideDateTime and GlideDate both support earlier dates so if the dates were manually entered, it would be saved. However, if the user opens the DatePicker, it will change the date to the current date and the date must be manually entered again.

Example:

Field "Date" is of type Date. I'm able to save dates "0001-01-01" and "9999-12-31" into the table.

However, if I open DatePicker on the field with value "0001-01-01", it will set it to today instead of "0001-01-01".

If I close the date picker, the date will be set to today so it's necessary to manually enter the date again.

To avoid showing datepicker, set the field type to "Single line text" and add date validation.