I'm using Calendar, the successor to iCal. I did use iCal before that. I carefully do Time Machine backups at least every hour. However, to my horror, I discovered that Calendar has its own strange way of backing up. Time Machine is useless for Calendar if you don't do the intermediate step of backing up. Then, Time Machine will help.
The intermediate step is to have Calendar open. Then go to Calendar>File>Export>Calendar Archive. This opens a window where you can designate where to store the archive file on your computer. I choose to put it in Applications right next to Calendar.app. Then, Time Machine will back it up. When Calendar crashes and everything is lost, you open the archive and it produces the data. I didn't know this when my Calendar crashed, but I fixed it as shown above in this thread. It was traumatic, but eventually successful. If I were doing a doctor's office, I'd make an archive every hour. You can always erase the old ones when they're no longer useful. I haven't bothered to look, but I'm not sure Apple has explained this trick. I consider it something of a boobie trap and I was the boobie. Why didn't they just stick in a Save button and update the app like everything else does?
