“I had completely forgotten an event in my life that occurred roughly 30 year before, until a friend asked me if I remembered it. Then suddenly, I recalled the the entire event.
So, clearly, it was not completely erased from memory!”
My wife and I are pushing 80, and we both have what you described.
A conversation, often on the phone with a distant relative or friend will trigger a forgotten memory.
Or something on tv triggers old memories.
One of our adult sons has an incredible memory from early childhood to his early fifties. He will bring up something that happened decades ago and describe it like it was a recent thing. That often triggers memories which have been buried for decades.
Even he suffers from what we call Rhino syndrome. That happens when you start to walk into another room to do something and forget what you were going to do. So, you shake your head and snort like a Rhino until your memory comes back. Or it is gone forever. Obviously, what you forgot was probably not that important.
Your Rhino syndrome has an actual name. It’s called the doorway effect. It has been studied and is a very real phenomenon. It happens to pretty much every one of us.
For more info: https://www.google.com/search?q=doorway+effect&ie=UTF-8&oe=UTF-8&hl=en-us&client=safari