We've had a lot of people complaining that a range of old appointments are missing from the calendar. For example, in November they notice appointments from July and earlier are still in the calendar but appointments in August and September are missing.
When all old appointments go missing AutoArchive is the most likely culprit, but AutoArchive doesn't delete recent appointments and leave much older appointments in your calendar, so we know that it’s not an archive problem.
Looking in my crystal ball, I see the a new handheld device was put into service right about the time of the first missing appointments and its being synchronized it with Outlook.
Because the appointments were deleted by the device and synced to Outlook they may not be placed in the Deleted items folder. If they are not in the Deleted items folder you won't be able to recover the items - you'll need to restore them from a backup file.
Typically, sync software defaults to syncing current appointments and deletes appointments older than a few weeks to conserve space, with a default setting of 60 days (8 weeks) or similar. When appointments are deleted from the handheld, the sync process deletes them from Outlook too. So after a few weeks of use, appointments are deleted from the handheld to free up space and then from Outlook on the next sync. The calendar will have appointments for dates before the first sync and very recent dates but the period between the first sync and a few weeks ago are missing.
Set the handheld to keep appointments forever. If you need to free up space on the device, use AutoArchiving in Outlook to remove appointments from Outlook. When you archive them, the next sync will remove them from your handheld.
On a Blackberry, open the Calendar, press the Blackberry button to expand the menu and choose Options. The setting that controls how long items are kept is near the bottom of the General Options page.
Items deleted in the sync process are usually not recoverable. If you don't have a backup they are gone forever.
Always, always back up your contacts and calendar when you get a new handheld and start syncing with Outlook. We see too many reports of disappearing appointments and contacts when users start syncing with a new device, even from people who are family with syncing. It's too easy to forget to change a setting and lose everything or end up with duplicates.
See Duplicate Remover Tools for Microsoft Outlook for additional options.