I honestly never knew, or paid attention to cans having sell by dates! So yeah, I'm sure I've used some old stuff!!
And yes - I've had PLENTY of days like that. Including the day (recently) I came home from grocery shopping (for the 3rd or 4th time because I kept forgetting the 1 thing I went for), and put the groceries away. Later that evening when I needed that ONE item I kept forgetting ... it wasn't where it belonged. I did find it, in the freezer. The item ... tampons.
Trust me, that was not a pleasant experience.