Besides the “Events with an invalid/valid date” addon rule, there is a Date addon gramplet from the Isotammi Group
The Dates Gramplet is installed in the Events list. It can be used to manipulate event date information, especially to correct dates in the wrong format. First select one or more events to which you want to assign the function and the desired correction function and press Execute. This can be used, etc., with the rule “Events with an invalid date” so that it first generates a filter that looks for invalid dates.
