It is weird what the brain does, it seems to park stuff in a deep vault until needed, though some things cannot be dragged up from that vault.
The way the brain seems to work is that if IT decides you don't need that stuff anymore, it sends it to the Vault, or worse, takes an executive decision to erase it altogether !
But long buried memories can be suddenly whooshed up from the vault by the strangest of things, recently I had this happen simply because of a smell ! Another thing that drags them back is meeting a long lost friend, who reminds you of many things you did, which had been in theory long forgotten by you.
I had this a while ago, I met an old mate from my teens, and he reminded me of one occasion where we had been on the Beer all night, then went for a Curry, and then I, as he recalled , but I had forgotten, in a car full of guys, I dropped the worst Fart any of them had smelt in their life !