There's actually a book about unreleased games, written by Frank Gasking, just about to come out (taking pre-orders as of today).

Myself and other team members were interviewed by the author, some time back, about one of the unreleased games I worked upon (Chips Challenge, NES).

[I have no affiliation with this publication, apart from being interviewed]

https://www.bitmapbooks.co.uk/products/the-games-that-werent