Are yes, I remember it well, and still use the triangular "spanner".The tins were always opened with a Tennants beer tin, "top-end". spanner....this instrument gouged out a triangular coupon which had to be bunged to prevent access of cockroaches and various other Beasties.
These tins were breached with a couple of dings with a sturdy meat skewer.
Just some old memories.
We used to sell a plastic triangular spout that you could put/jam in the hole to make pouring easier.
As evap was used for cups of tea it needed to last longer, so a smaller hole with the skewer or a nail slowed down it going off, and could be blocked off with matchstick or similar. I still use a matchstick in the salt cellar to keep it dry.