A quick tip, I found today that some iPads are missing March 2013 from the calendar. If you are, then check appointments for 1st April 2013 and if there are any all-day events booked, then remove them.
This issue is caused by a software glitch that has a problem with 1st April 2013 daylight saving change.
Removing any all-day events from your calendar , brings back March 2013.
Hop you find this tip helpful.