Funny thing if you ask me about dates of personal events
If you ask me off the top of my head the exact date any of my grandparents died, I cannot remember.
I can remember the month and year. I can tell you how old I was. I can remember exactly how I was told about their deaths and where I was. I can remember my exact reaction.
But I cannot remember the dates themselves without looking it up.
We remember the dates of birthdays and anniversaries because they are joyous events that we celebrate each year. We remember the dates of historical importance--September 11, 2001, November 22, 1963, December 7, 1941--because those are remembered by the general public and we hear about them on the news every year when that date comes around.
But dates of personal significance where the events are troubling or disturbing or uncomfortable, where there's no need to celebrate or remember on an annual basis....we don't always remember those dates. We don't want to dwell on those dates. We remember everything about that day, but we don't always remember that date.