Google Sync uses funambol technology. There is a rather limited sync window available. If you check the options for Sync, you'll find the largest window you can sync is one month in the past and 6 months in the future, based on the current device date. (At least that was the largest sync window last time I used Sync).
That's one reason I stopped relying on Google for OTA sync of my calendar. It is remarkably convenient for non-BES users, but too limited for my needs (I have years and years of past appointments on my device, over 4000 items right now).
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