Calendar entries are documents like any other in Notes, and documents do not "disappear". Either they are archived, or they are deleted, or maybe some function was run on them that made them be removed from the Calendar view, but they have not just gone to thin air.
You can find your Calendar entries in the All Documents view. Try searching there by date value. If you do not find them there, then they are no longer in the database you use. Check the archive, if you have one, or a backup.
Pascal.
I've got nothing to hide, and I'd very much like to keep that away from prying eyes.