Calendargirl I use this phrase, only for events which were family events and my memory of the event was corroborated by other family members present, usually by me mentioning the event but without saying my specific memories of it. I very carefully drew a line between those events, and those where I was entrely open to her interpretation or knew she was right. I fully accepted then as now that memory is fallible.
The problem is that DD has a very patchy and fallible memory and admits it. She will remember for years, a favorite dress from childhood, for example, and talk about it and then one day when someone mentions it, her mind is a complete blank and she cannot remember it, and can't even when shown a photograph and has never been able to recall it since. These memory lapses used to cause her real distress and there are now family memories, really lovely memories, which she cannot now remember and we no longer refer to when she is around, because it upsets her that she no longer has any memory of them.
But to return to the subject, I think these one off events are best treated for what they are, one off events, rather like the event described in another thread. They are triggered by a concatination of memories, and currents events in their lives at a given point and produce a sudden effusion of uncomfortable memories. At another time their view off the same subject may well be very different.Ask them whether they want to discuss the matter further and if they do not, let it lie.