Past events disappear from my iCalendar

It has been my supposition that my use of iCalendar would not only provide me a means of planning future events, but also would provide a bit of a diary of events in the past. It is disappointing to go back to days months ago when I know there were documented events that just disappeared. Yet days and weeks before and after seem to have events listed. I was curious and re-entered events, times, locations and while it "accepted" the first entry as soon as I entered a second event (two days later), it deleted, before my eyes, the prior entry. I note that I use iCal on my desktop (Ventura 13.7.7) and on my laptop (Sequoia 15.6) and my iPhone 15 (iOS 18.6), I think I am backing up all devices to the iCloud, and syncing (but maybe don't understand how to check that). Has anyone else seen this problem and are is there a solution?