[chaley]

I would consider adding 2 columns: one text column to enter the date and a composite column to display it.

You would enter the date using some version of a string that supplies the numbers and the desired format. Example:
Y,1984
YM,1984,12
YMD,1984,12,04
The template for the composite column would split the "list" into its component parts then reassemble them as desired. Something like:

program:
# date_string = field('#other_column')
	date_string = 'YMD,1984,12, 01';
	format = list_item(date_string, 0, ',');
	if format == 'YMD' then
		strcat(
			list_item(date_string, 1, ','), '-',
			list_item(date_string, 2, ','), '-',
			list_item(date_string, 3, ',')
		)
	elif format == 'YM'  then
		strcat(
			list_item(date_string, 1, ','), '-',
			list_item(date_string, 2, ',')
		)
	elif format == 'Y'  then
			list_item(date_string, 1, ',')
	else
			'Invalid Format'
	fi