It cannot work by any other way
If settings were not opened the control is nil, so just save without updating the control. As noone opened the settings noone will see the label or tries to see the label, so there is no reason to update it !
If the settings were opened, use the controls created calback, check for YOUR addon's panel and then update the description text of the label.
If it does not dautomatically update by changing the conrol.data.title or control.data.text value, try to change the control.data.title or .text attributes and then call control:UpdateValue() function, it should update the label's text then based on the data table.