Classic Tales from the Chronicles of Superman which may or may not actually happen.
These are not hoaxes, dreams, parallel worlds or OTHER.
Usually these tales diverge from then current continuity or history of the chronicles featuring familiar characters in different settings or circumstances - variations on the legend along a "what if" timeline posited by the myth makers and tellers of the tales.
External Links to Online Comics
Superman, CARTOON HERO!" by Jerry Siegel and Joe Shuster, from Superman 19, 1942. 
A Great Imaginary Novel! The Amazing Story of Superman Red and Superman Blue" by Leo Dorfman, Curt Swan and Geo. Klein with Kurt Shaffenberger from Superman 162, 1963. 
An Imaginary Shocker! The Death of Superman!" by Jerry Siegel, Curt Swan & George Klein from Superman 149, 1961.