ya db.. dont worry too much, just keep it in the optimal conditions. if u dont intened to use it at the moment and it is hot (like in israel ..lol) u can put it in the freezer, and then a day or two before u planning to use it put it in the normal cool place, and then before actually using it half a day will be good enough to bring the paper into perfect working condition.
like decklet says, u can keep paper much longer than on the box, if they are freezed, and if they are swimming in the rays of sun, u can gave up on them even if they are fresh from the manufacurer.
i belive that b&h knows how to keep paper in good conditions.