Thanks. My problem has been solved so far. What makes me wonder is why it took me almost two years to solve this issue. When I first installed Calendar, It generated four calendars without asking me why. Later, a calendar called "Calendarscripts" appeared on the list. And this one would take all incoming events. When I bought Bento, another calendar named Bento has been added to the list. I have never intended to operate five or six calendars. But Bento would also registered some events. **** knows what and why.
After registering for iCloud, after using me.com, most of the entries disappered. I can imagine who the culprit was because around 20 years ago all calendars in my company were completely lost except for the name of each. They had been connected to a central calendar and synced with it. When that central calendar had a crash, all calendars were synced with the successor. Since it had no entries, all existing entries were lost. Sync as sink.
Some months ago, I lost 3 of four videos and around 300 photos from my iPad while saving it to a new computer. In addition, many apps were crippled because they had been "synced" partly. If I had decided not to save anything, all items would still be there. I assume this is also a matter of syncing.
Apple should give better control to the users for the procedurs involved in "syncing".