Dates must be in the format YYYY-MM-DD
But you can enter YYYY only and it will display eg 1900.
You can also enter YYYY-MM without a day and that will display eg 1900-03.
There is an option to “Only show year” in the “TreePress Options” tab, which will then simply display the year.
You can’t enter anything else eg ‘ABT’, ‘BEF’ ‘Circa’ etc.