I am aware of the issue where several duplicate events have been added to the calendar. There seems to be an issue where other people can invite my week number calendar to events, and these will appear to everyone subscribed to the calendar. I have reported the issue to google (here). If you want this issue to be resolved once and for all, please add a comment in the thread to let Google know this is a serious problem. For a quick fix, you can unsubscribe to this calendar and instead start using Google's official week numbers (instruction above). Please be patient and I am confident this issue will be resolved. Thank you.