I don't disagree with this. but that it why I mentioned "creative content," rather than "story." Because in the case of Gwenpool, my gut said that the cover of the Secret Wars issue is the important book, and it's not attached to a story. "Creative content" as I see it, is not something that's used to sell comics, but would be the thing that you're buying a new book for.
That's why I see the Marvel Age previews (such as Darkhawk) to be not as important as the comic that the story appears in. Even though the exact same content is printed, in Marvel Age the printed content is in service to advertise the upcoming book, and in Darkhawk it's the thing you're paying for. Similarly, the Liefeld Sketchbook serves as information of what you can expect if you buy an upcoming issue of New Mutants.