It took some time to get a really honest answer for jams & jellies stored on the shelf at room temp. Most said 1 year, some two. Only a couple pointed out, as above, that such preserves can (under good storage conditions) last almost indefinitely. If their seal is air tight so they are not exposed to germs in the air, and if the seal is very durable and remains undamaged, then the acid in addition to the sugar which preserves are loaded with and which is an excellent preservative, preserves can last years.
It seems obvious to me that the reason few have the courage to say that is that merely saying it might expose them, they fear (I think) to legal problems should someone open and eat their 10 year old strawberry jam. It is very possible that could be ok, but only if very specific conditions have been constantly maintained throughout the 10 years with a guarantee that no one has even slightly attempted to open it even once in that period. So . . . can't you just see the problems if you do not put all kinds of red flags around your statements when you mention that preserves can last a real long time? In today's litigious environment, I don't blame them one bit for refusing to commit themselves to the possibility of preserves lasting more than a year or so.