In Action Comics #265 (April 1960), Supergirl exposes her existence to Smallville and Superman doesn’t want that to happen yet. So he digs up some old Gas Z “Amnesia Gas”, which he had once buried outside of Smallville as Superboy. What’s interesting here is not the over-use of amnesia-as-a-convenient-means-to-revert-to-the-status-quo, but the back-reference to earlier Superboy continuity, throwing back all the way to Adventure Comics #235 (Feb 1957), a full three years. The editors over at DC seem to be intensifying that solid continuity that readers are asking for. This is the first time I’ve seen them reference a specific issue from years in the past.