But what if I wanted to have all the appontments backed up in the MyPhoneExplorer DB but only future +30 days in the past on the phone, like I can have it with Outlook of Google Cal?
This would make sense, but its easier to use and to understand that MyPhoneExplorer shows the content which is also on the phone. If you have to keep a large amount of appointments you can sync with a third-party-tool.