Deleted the following:

• In the 1940s Superman radio program, Supes' voice actor Bud Collyer was going on vacation and The Powers That Be needed a way to cover the lead actor's absence, so they came up with an idea: what if there were these strange green rocks that could make Superman sick? This allowed the groans of the ailing hero to be portrayed by someone else. Kryptonite became a Canon Immigrant some years down the line.

This trope is about in story explanations that justify real life casting changes for the same character. In the radio show, when Superman was sick from Kryptonite, another voice actor came in and played Batman making this at most a Suspiciously Similar Substitute.