Pundip I never understood why we can't add a full championship to the calendar. The only reason that I could think of is to avoid having dead championships filling up the calendar.
Are you talking about events with multiple dates? It's a limitation of the forum code, it only allows you to set a start and end date for the Original Post. So you could say... set an event's start date as June 20th, end date as August 15th. But that doesn't really tell anyone the actual dates of the races, just how long the series will last.
There is no option for multiple dates or a recurring checkbox option.