I was just about to create a thread for this same issue. I was trying to add Forza Motorsport 4 to a stack, but I can't find it via the stack game search or the main site search. Yet it has a valid link: https://www.gamespot.com/forza-motorsport-4/
@angerawr: Yes I am able to get to the page, but when I search for Forza Motorsport 4, it doesn't show up in search results, thus not allowing us to add the game to a stack. Here is a search link with "Forza Motorsport 4" as the query: https://www.gamespot.com/search/?q=forza%20motorsport%204
You will notice all the other Forza games, but not 4.