Older dates for CiviEvent
As you have discovered Jenni, changing any of the start offset and end offset values in the date preferences settings do not reflect participant and event dates.

/civicrm/admin/setting/preferences/date?reset=1

So unfortunately, there is no option to make these amendments via the UI.

However, CiviCRM does allow you to manually input dates/years well before 1999/2009 which are accepted, and the records do get saved without an error –





The same method also works when importing participants.

This is a sample CSV I’ve used which had a registered date of 1966 which imported successfully –