Profile: gerhardR-2

Problem: I would like to use a datepicker to select a date before 1583.

Solution: It's not possible to use Toolset's datepickers to save dates outside of the date range 15/10/1582 to 31/12/3000, according to our developers.

I think one alternative approach here would be to use a Number field instead of a datepicker field. If you only need the Year, that's pretty straightforward. However if you need to save a full date (year, month, day), it will require more information. Toolset datepickers save epoch timestamps in the database, so you could use the same approach.

Date: 28/01/1582 0:00:00 GMT
Epoch timestamp: -12241756800

So to save the date Jan 01 1582, you would save -12241756800 in the custom field.

Then you could use a custom shortcode to format that custom field timestamp as a date using PHP.

Relevant Documentation:
https://www.epochconverter.com/
https://codex.wordpress.org/Shortcode_API
http://php.net/manual/en/function.date.php
http://php.net/manual/en/function.strftime.php
https://toolset.com/errata/toolset-datepicker-date-limitations/