As I said above ...
But they were brought into continuity by the Superwoman/Kristin Wells stories. Said issues made Miracle Monday canon. Miracle Monday had references to Last Son of Krypton which made that canon, too.
Maggin's novels
are in canon. But not because he's such an integral part of the SA. It's because the comics directly reference his novels that they're canon.
Certainly, Fleischer's encyclopedia clearly stuck to the published comics and didn't consider anything outside of them to be canon. The comics-referencing-Maggin's-novels reasoning the same kind of rationale for inclusion.
The radio shows, movies, etc. wouldn't be canon since they aren't directly referenced in the comics.