It's important to make sure your play history is always properly recorded. Be aware of any changes to your ranking, any tournaments in which you're reported as a participant, and any events that you did not attend or that have been recorded with inaccurate information. If you learn that an event has been falsely recorded, be sure to report it. Failure to do so can lead to action against your account including event invalidation or permanent suspension from the DCI.
If an event is missing from your tournament history, be patient. Events can take several weeks to be fully processed. If your event doesn't appear after two weeks, contact the event organizer. If they are unable to assist you, you can appeal the event using the Event Corrections form here.