[PG-HQ Dev Blog] 2012 June Update

[Shad]

He has no say in the matter. Game mechanics cannot be copyrighted. So long as you don't use original AP artwork, you can make (and sell!) as many scenarios as you want.

Actual relevant U.S. law is FL-108 and reads as follows:

Copyright does not protect the idea for a game, its name or title, or the method or methods for playing it. Nor does copyright protect any idea, system, method, device, or trademark material involved in developing, merchandising, or playing a game.

It goes on in more detail, but that's the gist.

So long as you don't use PG artwork or quote passages from PG scenario books or rules, you can freely design scenarios and sell them as you please.