I think that it was Chris Covell who debunked the old magazine screenshot that was supposed to be Strider for SuperGrafx.
I don't doubt that it might have been worked on, but it would be very unique by unreleased PC Engine game history to be one of the only ones to have never been shown in any form.
Even games that were never up and running, like RPG Genjin, had multiple screenshots making the rounds.