 If worlds are concrete particulars (“I and all my surroundings”), as they are for David Lewis (1986), then we could say that a proposition is true at a world if the proposition is about the entities that are parts of that world and is true, and true in a world if true at a world and also part of that world.  There may well be difficulties of explaining how a proposition could be part of more than one concrete world (and why it would only be part of some concrete worlds but not all), but this framework seems to make conceptual room for the possibility propositions being true at worlds without being true in them.  