"Well, Sonny, I'm no Sam Spade.
I don't work any miracles,
And uh, I don't break down any doors."
'The Name Of The Game'
["Love-In At Ground Zero"]
This quote by private eye Ed Wallaby is all I have (so far) on which to base my claim that Sam Spade, the main character of "The Maltese Falcon" by Dashiell Hammett, exists in the main Toobworld* as well as in BookWorld, the Radio Universe, and the Cineverse.
It is standard practice for the Toobworld Dynamic (and, I suspect, for many of my crossover comrades working in the universes of other media) to accept references to characters and events from outside of the home turf as being a part of that particular bailiwick - so long as there is no mention of the source material. In this case, it means Sam Spade exists in the main Toobworld even though he has never been portrayed in Earth Prime-Time*.
* Sam Spade does show up in a TV dimension - 'The Strange Case of the End of Civilization as We Know It' exists in the Doofus Toobworld.